One plus 9r call, no sound.

0 1 Enter the setting interface of mobile phone system, and click "Sound and Vibration" in the options below.

Enter the sound and vibration setting interface to see if "Mute" is turned on. If so, close the right slider.

After turning off the mute, adjust the volume appropriately below.

There is also a shortcut, which is to enter the notification bar of the mobile phone and turn off the mute button in the button.

If none of the above works, you can restore the factory settings.