iPhone 8 call issues

I have a persistent problem with the call quality of my iphone 8. People often say they cant hear me properly - the sound is muffled, it goes quiet - sounds digitised sometimes.. not the whole call, but for 2 seconds or so.. but its a persistent issue.

Its unusual as i havent had this issue with any other phone before.

So when ive had somone on the other side of the phone say - "can you repeat that" - "sorry the call went quiet" - "you sound muffled there" - there is an issue.

I have been to the genius bar - and i was advised to set up as a new phone - which is a real pain as i have to install all my apps again - set up passwords on banking apps again.

This is not great - anyone else had this issue?

I will repoert back if the reset and set up as new works.. my genius bar person, was pretty ambivalent to the issue, and im sure there is a problem out there - but we shall see.