Other person can't hear me

[nzpassat]

For any outgoing or incoming calls, the other person can't hear me. I can hear them fine, and it's been working fine for ages. I thought it was maybe my phone but I got the same issue when I tried it with my wife's phone. I suspect it is possibly the car's microphone.
Is there a way to work out what the issue is? I have obd 11 which didn't show anything.
My car is a 2016 rline bitdi 4motion sedan.