Chosen Solution

Hey Guys, I have a 6s iPhone. Its microphone works properly during video recording, sound recording but when I make a call it is unbelievable quiet. I tried to reset the phone in all possible ways, but nothing helped me. (nor disabling the Phone Noise Cancellation option) With iOS 11 I had the following experiences: the microphone was quiet, and while I moved my phone sometimes the microphone was totally mute. Then I updated to 12. Now I have a continuous record but it is soooo quiet, nobody can hear me. What is the source of it? Any solution?

As Daniel said make sure the whole for the mic is not clogged up. If that fails then the mic will need to be replaced as it’s starting to fail.