Some times when I call someone they can not hear me. But if they call me they can hear me.

[AC Question]

I have a samsung galaxy s6 cell phone on sprint network. Some time when I call someone they can not hear me. I have called them back and they still can not hear me. If they call me back they can hear me and they always hear me on incoming calls. What is the problem with Samsung s6 phone on sprint network.