why do we use phrasal verbs in English?

Solution 1:

We use a phrasal verb (e.g. put down to) instead of its single-word equivalent (attribute) for the same reason that we choose between any words with similar meanings (e.g. start/commence, lots of/numerous):

Namely, we choose the word to fit the context. Phrasal verbs are generally more appropriate than their single-word equivalents in informal contexts such as everyday conversation. You run the risk of sounding pompous or pretentious if you limit yourself to single-word verbs.

Furthermore, there are many phrasal verbs that do not have single-word equivalents. Here are a few examples:

• We spent a week living it up in the luxury of the Intercontinental Hotel.
• He was afraid the others might think he was showing off.
• I wouldn't put it past you to hop on a plane.
• The problem was how to sweat out the next six weeks.
• He worked hard and was easy to get along with.

And in some cases the phrasal verb adds a layer of meaning that is not present in the single-word equivalent. For example:

• What did you get up to (= do) while I was away?

The Collins Cobuild Dictionary Of Phrasal Verbs explains:

When you talk about what someone gets up to, you are referring to what they do, especially when it is something you do not approve of.

Note: All example sentences are from the Collins dictionary.