When did "brick-and-mortar" become a set phrase?

Solution 1:

As far as I could find the phrase brick and mortar meaning the provision of services in a building with human staff as opposed to computer-based service provision gained currency in the 1970s, mainly in the banking industry. Use of phrase in opposition to mail-order business appears to have started slightly later, even though mail order had been around for a long time. This Ngram shows brick-and-mortar branch and electronic bank taking off in the early 1970s (earlier instances of electronic bank refer to data banks); brick-and-mortar store does not take off before the mid 1990s. The earliest instance of brick-and-mortar in this modern sense I could find is from 1971, but applied to libraries though. And a charming thought it is:

Although claiming no gift of clairvoyance, I, too, can foresee a time when today's brick-and-mortar library will be obsolete. Our primary source of knowledge will be electronic information nodes or communications centers located in our homes, schools, and offices that are connected to international, national, regional, and local computer-based data networks.
Miller, Arthur R., “The Assault on Privacy: Information Technology―a Study of Good and Evil,” Law Quadrangle Notes, V. 15, Iss. 02 (Winter 1971) [full access]

Then, still in the realm of education, there is this one from 1974, or maybe later. When Google has several volumes or issues of a magazine together they give the date of the first issue.

[…] many courses, but not all, could be taught by a combination of two-way interactive instruction combined with extensive use of film and assisted, of course, by a computer terminal. There is no reason for a student to travel to a ‘brick and mortar’ type of institution to get this kind of instruction.
CIPS [Canadian Information Processing Society] Computer Magazine, vol. 5, issues 1-11, 1974, p. 96.

It was in the banking industry though that the phrase came to be more widely used. From the early 1970s banks started to offer banking services from ATMs and CBCTs (costumer-bank communication terminals) often away from their brick-and-mortar branches:

In November the Comptroller issued a new CBCT ruling, declaring that if CBCTs are branches, they differed from traditional brick-and-mortar branches and can meet less stringent establishment procedures,
Computer Law and Tax Report, vol. 2-7, 1975, p. 155. (computer “brick and mortar” 1970-80, #6)

The phrase pops up several times in U.S. Congressional hearings on the new electronic banking. This exchange took place in a hearing before the 94th Congress, so no later than 1976:

Mr. Bartell. Just on this point, though, are electronic terminals a substitute for or an alternative to brick and mortar branches? [p. 133]

Senator McIntyre. Dr. Mann, in Chicago we were told that electronic transfers were being widely accepted by the public at large, and they will make brick and mortar obsolete. [p. 400]
Federal branching policy: hearings before the Subcommittee on Financial Institutions of the Committee on Banking, Housing, and Urban Affairs, United States Senate, Ninety-fourth Congress, second session

Early in 1977 Toni Wiseman reported on further hearings in “EFT Unit Asks Limit on Federal Access,” Computerworld, Vol. XI, No. 9, February 28, 1977 [full access]:

Washington, D.C. ― Legislation should be enacted giving individuals the right to contest any government access to their financial information contained in electronic funds transfer (EFT) systems, according to an interim report released by the National Commission on EFT here last week. [p. 1]
[...]
The report recommended rules regarding the deployment of off-premise EFT terminals should be distinct from and less restrictive than those for "brick and mortar" branches. [p. 4]

Four years later, some people had grater expectations from e-business already. Here’s Desmond Smith, “Info City―New York Is Now the Information Capital of the World,” New York, February 9, 1981 [full access]:

A revolution is brewing in New York City: information is taking over. The revolutionaries are the people who have learned how to exploit the new micro-technology of computer-linked communications to the fullest: manufacturers who own no workshops, bankers who handle no cash, retailers who advertise goods “not available in any store,” and businessmen and women who “talk” to work rather than ride. (p. 24)
[…]
The electronic bank is replacing banking in the bricks and mortar sense everywhere, and it’s a lot cheaper to operate. (p. 26)

The earliest unambiguous instance I could find of brick and mortar as opposed to mail-order is from 1980 in Dun's Review (I checked here that the date is correct). There’s a possible instance from 1975, but I didn’t manage to check the context or the date itself. So it looks as though the phrase gained currency in the banking industry in opposition to computer-based service provision, and was then borrowed into the mail-order business context.

This idea that computer technology was going to reduce the need for brick-and-mortar was around in the 1960s already, but for a different reason: computer technology required less labour, and hence smaller facilities. So in the following quote brick-and-mortar is not used in the modern sense of alternative to e-business. But there is an opposition between computer-intensive and brick-and-mortar-intensive production systems that likely paved the way for the modern use of the phrase. The snippet Google shows is incomplete, so I combined it with the main output page. I checked here that a Univac III computer was delivered to Esquire Inc. in August 1963, so the Google date is correct:

Solution 2:

History isn't my strong suit, but as I recall, the phrase bricks and mortar started becoming a set phrase as an antonym to online shops around the time that internet startups began to take over very well-established incumbents in their area of business.

Here are a couple of articles from 2011 about how the bookshop Borders failed while Barnes & Noble survived in the context of online bookshops like Amazon:

• Goodbye to bricks and mortar
• Why Borders Failed While Barnes & Noble Survived

For comparison, Encyclopaedia Britannica's 15th edition of 2010 was its last print version. It would therefore seem that the term entered common usage around 2010 to 2011.

We can dig deeper, though. If bricks and clicks can be considered a derivative phrase of bricks and mortar, then any date for the popular usage of bricks and clicks would be an upper bound to that of bricks and mortar. The book Anytime, Anywhere: How the Best Bricks-and-clicks Businesses Deliver Seamless Service to Their Customers was published in 2002 according to Google Books, and Ngram indicates first usage just before 1990, with a spike in the mid '90s.

Adding the phrase bricks and mortar business to the Ngram search is revealing. There's a spike around 1950 and a smaller one around 1970, and another large and sustained spike starting around 1990. Scanning a couple of samples briefly, the pre-1950 usage seems to refer to land-vs-sea 'products' - e.g. "... said it was only in recent years that the Admiralty had diverted its attention from the building of ships to bricks and mortar. ..." (Navy Estimates, 1904-5). The 1970 usage seems to be to the presence of many buildings - e.g. "Employees like to be near the major stores, they like the amenities, ...". The early 1990s usage seems to be similar - e.g. "We are not in the bricks and mortar business, we are in the people business."

The later 1990s usage starts to acquire the antonym-to-online sense, for example,

a recognition of the fact that income generated by intangibles, like interest income, is easily portable and can be moved offshore without the significant physical commitment that would attend moving a traditional "bricks and mortar" business. - Electronic Commerce and International Taxation - Page 339

Finally, if we look at actual e-commerce, wikipedia suggests that Pizza Hut was the first bricks and clicks business, with a pizza ordered over the internet from a physical store. The article doesn't provide a date, but socialnewsdaily.com helpfully dates it to a Pizza Hut tweet in 2013 referencing the event in 1994. As the first appearance of e-commerce, it would be reasonable to consider the date of its appearance to also be a lower-bound to the date of its antonym.

You ask:

When did "brick-and-mortar" become an "antonym" of e-commerce?

Based on the above, it would seem that this can be dated back to the mid-'90s.

I don't have an answer for your second question regarding catalog-merchant sales, but that investigation sounds like a whole 'nother story. :)

Solution 3:

The bonding between bricks and mortar traces back to the days of Pyramids or even prior to that. The Free Dictionary citing The American Heritage dictionary refers 'Brick and Mortar' as basic, essential — something physical of this existential world as in Mathew Arnold's essay (1865): "Margate, that brick and mortar image of British Protestantism". It is evident here that phrase has assumed a metaphoric characteristic wherein essential building materials seem to convey matters of greter import of the physical world.

Idiomation confirms that sometime between 1995-'97 the expression 'Brick and Mortar' store was understood by most people to mean a business that did not have an internet presence(e.business) and was doing business in the traditional way. In an article by Anne McCrory: Gibberish Arising from the Web:Dot-com your Brick and Mortar biz (Computer World,March 22, 1999) she is of the view that 'brick and mortar' has been around since the dawn of technology in distinguishing between the real and the emerging— say,the brick and mortar bank branch vs.the electronic unstaffed ATM kisok. But the new meaning of brick and mortar as opposed to the new piece/the ethereal piece/ the e.store/ the on line store/cyber store was just in the air eluding understanding. Uptill now, B & M is just a metaphor suggestive of something of the physical world. It has not evolved into an antonym as yet. Interesting to mention that Copy Editor(vol.11,yr.2000) refers to 1994 usage of B & M as formal structure as opposed to cyberspace.

Strictly speaking, the origin of the internet dates back to 1960s. Thanks to the uphill initiative of the USA, the UK and France. 1980s actually mark the beginning of the transition to the modern Internet.

In his 1984 path breaking novel, NEUROMANCER, William Gibson was able to use brick and mortar ideas to the realm of cyberspace.

A push towards opening the technology to e-commerce is an event from tha mid 1990s. The Harvard Journal of Law and Technology (vol.16,Number-I,Fall2002) presents a kaleidoscopic view on evolution of Internet metaphors- the intenet as Conduit : the information superhighway to 'cyberspace' down to ' Internet as real space. It could have been better if can provide you the 'link' but I fail to. The article presents an interesting reading.

So we can safely attribute that somewhere in the last half of 1990s the internet has evolved into a real space as opposed to B&M. Better we would ascribe it to William Gibson from the date of publication of the ground breaking novel Neuromancer where cyberspace connoted not only a new space but a space so dramatically different from real space— BRICK AND MORTAR space.The date cannot be pegged.

Solution 4:

(First Question) Though e-commerce began in the late 1900s, the term brick-and-mortar probably started becoming the antonym of e-commerce in the past ten years or so as discussed in this article from last year. (A hardware store owner notes major shifts in business from brick-and-mortar to e-commerce in the past 10 years.)