A number of Pixel 3 and 3XL owners have reportedly taken to the Google Product Forums to complain about issues with voice-calls on their devices. These problems apparently include low-quality in-call audio, connection issues and more. On the other hand, there are claims that the December Android 9.0 software update is a solution in some cases.
https://www.notebookcheck.net/Pixel-3-and-3XL-users-allege-call-quality-issues-in-their-phones.384926.0.html