It could be incompatible. There are about 10 different charging ports made for this Galaxy s6 and its variations. If the wrong one from the wrong network is put in sometimes cables don't reach and additional problems due to a mismatch may occur.
The void spaces in the device's frame allow the correct board and board components to fit. Correctly matched parts allow the mother/daughter board to fit flat (as designed) and go back together once you are done replacing parts. If a mic does not match up to it's hole through the frame, you might block sound. Look at the frame to the right of the charging port while the screen is face up. If that hole is clogged it should be cleaned. If the sound quality improves, than I would probably consider opening it up to clean the inside of the frame and the mic.
One more thing. A microphone actually. With your phone's back side down, viewing from the top, there is a microphone hole just to the left of the infrared blaster. I do believe this one is attached to the motherboard.