If it’s a corporate phone, it could be the MDM and/or MDM policies that are the culprit. Or it could be a pre-loved phone, which companies issue without telling end users.
Neither.
However, thanks to your post I started thinking more about apps and right about the time his issues began, about the time everyone started working remote, we were offered an app to interface with our corporate phone system and I didn’t bother, but he did install it.
This app is pretty flaky and sometimes the connections seem to be compressed severely and it sounds like I’m talking to a chipmunk. So, I’m going to try to help him get rid of that app and see if matters improve. Thanks!