hear backvi phrasalphrasal verb, intransitive: Verb with adverb(s) or preposition(s), having special meaning and not taking direct object--for example, "make up" [=reconcile]: "After they fought, they made up."
(receive a response from [sb])
收到回复
I left him a voicemail inviting him to the party and I'm waiting to hear back.
hear back from [sb]vi phrasal + prep
(receive a response)
收到…的回复
I sent my friend an e-mail and heard back from him immediately.