The problem is not software, is the location of the earpiece, is in the flip camera module, a little hole. You ear never go directly to the speaker in this phone, so don't expect a solution for the this unfortunately. The other phones have a pop up camera like xiaomi 9T or oneplus 7 Pro, have the speaker in the middle of the phone like all phones, and not in the camera module like the zenfone 6. The only solution to better soud is in a call flip the camera, turn the phone and put your ear near the hole of the flip cam open. I don't understand how a brand like Asus sell they top phone witout test the main function of the phone, the simple call!!!
If you read in the internet have hundreds of owners of zenfone 6 claim this issue. I don't know how asus go solve this problem, its nit a software problem, is a hardware /mechanical problem so the phones need come to factory..
