Why can i hear people on my phone but they cannot hear me? What do I need to do?

[AC Question]

I call and they answer and cannot hear me. I answer their call and they cant hear me. What's going on and how do I fix it?

 

[B. Diddy]

Welcome to Android Central! What phone? Does it work on speakerphone or wired/Bluetooth headphones? If so, then there's probably a problem with the phone mic.

 

[lashh5]

So if there is a problem with the mic, can it be fixed or is a new set recommended to be purchased?