why does my HTC One have static when I use the phone but not when I use the speaker?

[AC Question]

just today it started, that when I use the phone either call someone or receive a call, all they hear is static until I turn on the speaker and then it is like using the speaker system.

 

[B. Diddy]

Welcome to Android Central! Can they hear you if you use a headset as well? If so, the primary mic is probably faulty.