phrasal idiom vs locution

phrasal idiom and locution both are nouns.

Word	Noun	Adjective	Verb	Adverb
phrasal idiom	Yes	No	No	No
locution	Yes	No	No	No

As nouns, locution is a hypernym of phrasal idiom; that is, locution is a word with a broader meaning than phrasal idiom:

phrasal idiom: an expression whose meanings cannot be inferred from the meanings of the words that make it up
locution: a word or phrase that particular people use in particular situations

Other hypernyms of phrasal idiom include expression, saying.

phrasal idiom (noun)	locution (noun)
an expression whose meanings cannot be inferred from the meanings of the words that make it up	a word or phrase that particular people use in particular situations