I know this thread is old, but the issue is still happening. I just recently experienced the same issue with my S5. People couldn't hear me unless I was on speaker or Bluetooth. I read somewhere that a guy took an air compressor and used approx. 30 psi to blow out his microphone. First I tried a factory reset, but that didn't work. So I tried the air compressor and held it directly against the microphone for approx. 10 seconds. The issue went away immediately. I guess since the port is so small that it's easily clogged???Many people I am talking to using the phone mic complain that my voice is garbled, but as soon as I switch to speakerphone the problem goes away. This is common on both S5's I have.