What is the difference between an expression and a phrase?

Solution 1:

Simply put, an expression is more like a saying, an idiomatic way of expressing something in less literal, less familiar terms:

How do you do? is just an expression: you don't expect someone to actually tell you how he is doing; he should just say how do you do? back, because it means little more than "hello".

A phrase is just any sequence of words, usually less than a sentence:

• rip them out
• even the Aztec women
• before the Spaniards
• reloading muskets
• because they could never have continued their rituals without capturing large numbers of enemy soldiers (this one is dubious, because "clause" would be a more specific and thus better name)

A great many expressions are also phrases, like put behind bars or heaven forbid.