Microphone working only when loud speaker mode

Hi,

Is the phone in a protective case at all?

If so remove it from the case and check if it now works OK.

If it isn’t in a case or it still doesn’t work OK when out of a case, try using a vacuum cleaner to clear the microphone voice inlet hole located on the bottom edge of the phone in case it is blocked by dust or lint etc. Do not use a pin or probe to try and clear it as the microphone is behind the hole and may be damaged.

Here’s an image of the phone showing the location of the two microphones used in the phone. The one on the bottom edge (highlighted in red box) is used for normal calls. The one on the top is for loudspeaker calls.

(click on image to enlarge).

If still no good try wiping the cache partition in case it is corrupted data affecting the microphone’s operation.

If still no good try using the phone in safe mode and check. If it works OK in safe mode then a downloaded app is the cause of the problem. The trick is to find out which one.

If still no good the phone will have to be opened and the microphone connection checked etc. Here’s the ifixit Samsung Galaxy M31 guide that will help to open the phone to gain access to the microphone etc