People I call won't understand me

[Aphexx]

Hey there! 

When I take a call, the respondent barely understands me. First I though that the microphone might be broken - BUT Voicemessages with WhatsApp are no problem, as well as calls with my headset and even calls with the loudspeaker turned on. As soon as I turn the loudspeaker off the call silences as if a noise-sensor waites for loud input - shouting works. Any ideas? 

Thanks

[pseudonym]

That's pretty strange. Short of a reset, you could try the following:

*  Download another phone app and see if it works better.

*  Go to Settings app, then Apps& notifications, then App info, then Phone. Under Storage, clear out first Cache (see if that's enough), then Data (if necessary), and see what happens.