How do i fix the mic on gallaxy s4 it only works on speaker phone

[AC Question]

When someone calls I can here them but they can't here me talk unless I put the phone on speaker phone

 

[B. Diddy]

Welcome to Android Central! Your primary mic at the bottom of the phone is either blocked for faulty. Do you have a case on? If so, make sure it doesn't block the mic opening. Also, inspect the opening carefully to see if it's clogged by debris. If the opening is clear, then the mic is faulty and needs to be replaced. Bring it to a repair shop.