I have exactely the same thing.
On tegular GSM with full 4g réception people hear one word over 3 !! It s total crap. In the 90s phones where better. They hear you like a robot too.
When on lound speaker the samething happen.
The strange thing is that it works better on Signal or whatsapp!
What I noticed is as soon as I give a GSM call it goes on 3G like it is loosing signal. Then when I stop the call I get back to 4g.
I suppose there is a problem in priorities… With pixel 4a my 4g tethering would drop when I received a phone call (which is not nice), but at least I coule pickup the phone and discuss!
I have a lot of call that don t even ring too.
I am in france on free mobile, changed my SIM card.
Was worki g on pixel 4a and samsung a3 2017.
Make this phone work !