1. Check that your microphone is not muted.
2. If there is any background noise, move to a quieter area.
3. Check if the issue is happening with a specific phone number on outgoing or incoming calls.
4. Connect a compatible wired headphone that has a microphone. If the headphone works, remove them to continue troubleshooting the internal microphones.
5. Restart your phone and test your phone's microphone and speakers with any free Voice Recorder application available from Store. Record an audio clip and play the recording. If you can hear the recording, your microphone is working.
6. If the problem persists, locate your phone's microphones and check that openings are not blocked. To find the microphone openings, see your phone's user guide.