How do I fix calling related sound issue on my iPad?

Clear the microphones

1. Remove any screen protectors, films, or cases from your iPad.
2. Clear any debris from the openings of your iPad.

Test your microphones

1. Open the Camera app.
2. To test the front microphone, record a video of yourself speaking while facing the camera on the front of your iPad. 
3. To test the back microphone, tap the camera chooser to switch to the back camera. Then record another video of yourself speaking while facing the camera on the back of your iPad.
4. Play back both videos. You should hear your voice clearly in each.

If your voice sounds muffled on iPad Pro (M4), iPad Air (M2), or iPad (10th generation)

If your voice sounds too quiet, or muffled, when you play back the videos you recorded using the Camera app, make sure that the microphones on your iPad aren't blocked by your hands or a case. If your iPad has a screen protector, make sure that the screen protector has an opening over the front microphone.

If the microphone doesn't work in a specific app

1. Go to Settings > Privacy > Microphone.
2. Make sure that the app is enabled.
3. If the app has permission to access your microphone, or if it isn't listed, contact the app developer.

If you still don't hear your voice clearly, contact Apple Support.