I mean, when somebody has called you on the phone but you cannot hear their voice, can you say that their voice is not hearable? Then the answer is yes you can.

Somebody can also be replaced with someone in that sentence and you can replace the words has called you with calls you and the word but with the word and. You can also change the word hearable to the word audible. Then it would read this way:

I mean, when someone calls you on the phone and you cannot hear their voice, can you say that their voice is not audible?

Hope that helps.

I can’t hear you.

or

I can hardly hear you.

yes it works