Hi there![]()
I assume by "set phrases" you mean what I usually call "collocations", that is, words that are commonly used together (and which can vary wildy depending on region and/or dialect). They can be verb-noun combinations, adjective-noun combinations, preposition-noun combinations or virtually anything really. Google some English collocation sites for practice! Some examples:
take a bath
make a promise
decisive action
innocent bystander
Idioms are different in the sense that they usually have both a "literal" meaning and an "idiomatic" one. Idioms do vary regionally as well but rather than one word being different in the phrase, usually a completely different idiom is used or is not used at all. Many phrasal verbs are idiomatic as well. Example:
He picked me up
literal meaning: He lifted me off the ground
other (idiomatic)meaning: He asked me out on a date
other (idiomatic) meaning: He gave me a ride in his car
Hope that helps!![]()
Fiona

Student or Learner