I know that this post is very old, today I have flashed my moto g6 play (sprint) with a ROM to upgrade my cellphone from Android Oreo to Android Pie due to the long delay on getting an officiall update, after the flash everything works as expected except the calls: the microphone and speaker seems to not working only during calls, after some research, I found that the "modem" image is the responsible of my problem, so I flashed the modem image from the old ROM stock (Android Oreo) and now It works. Note: I do not know if this will work with another version/model, I've experienced this situation with a moto g6 play (sprint).