An Idiom is a group of words whose meaning is different from the meaning of the individual words. Therefore, an idiom is a phrase that doesn’t translate literally into a different language. Many phrasal verbs are idioms, but not all idioms are phrasal verbs. Apparently, there are over 25, ooo idioms in the English language.
An example of an idiom:
I am feeling under the weather. Means, I am not feeling very well.
So, you could say a phrasal verb is an idiom that is a verb.