The Google Pixel 3 (and 3XL) have had widespread reports of call quality issues. I can confirm that mine and my wife’s phone are both affected by this, where the person on the other end can’t make out what you are saying until you restart the phone, after which it’s fine for anywhere from a few hours to a few days before happening again.
We have had one phone replaced under warranty (no one else has been successful with this approach, but I figured I’d try anyway) and unsurprisingly the replacement device has the exact same issue.
There are literally hundreds of reports online, which is likely to represent just a fraction of those really affected, and Google are refusing to acknowledge the issue or accept complaints, and still continue to market and sell the phone in Australia even though it technically would be in breach of Australian Consumer Law to continue to market and sell a phone that cannot be reliably used to make calls.
Multiple attempts by myself and others to hold Google to account have so far failed, but I do not want to give up because that’s what Google will be counting on. They do not have a complaints process, so all correspondence goes to a helpdesk team who either cannot or will not escalate to their management.
This has been extensively documented here - https://issuetracker.google.com/issues/124412355 - and shows that the problem really is widespread and not specific to any mobile carrier or country. Reports in here also suggest that Google are offering a single device replacement (with another faulty device) to customers who report issues, but that is where their offer is ending. I have not verified this myself, so cannot confirm if this is the case.
In my view, this is a shocking display of arrogance and contempt for their customers and reminds me of the 2010 iPhone 4 “grip of death” issue that Apple originally tried to deny.
I have reported this to the ACCC and The Office of Fair Trading in QLD, however they also did not seem determined to assist with this, which I found extremely disappointing.
If anyone else is having these issues, it would be great to coordinate an effort to have this matter escalated as high as possible to get the attention it deserves.