@Sparkle53: If you have a case or cover on the phone, please try removing it temporarily to see if you notice an improvement, as it may be obstructing the in-call microphone. If this isn't applicable, try placing the call on 'Speaker', and check if this makes your voice come through more clearly.
To test the hardware, please head to the Samsung Members app > Press and hold on the app icon > Diagnostics > Mic. During the first test, hold your phone as if you were on a call, then speak in a clear voice. Are you able to hear yourself during the playback?
