iPhone issue
I can’t hear the voice of the person on the other side on call
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Can't hear at all, or too quiet?
Too quiet - press the Vol Up button during a live call.
Can't hear at all - restart the phone, Reset network settings in Settings, general, reset.
click here: If you hear no sound or distorted sound from your iPhone, iPad, or iPod touch speaker
Or arrange a repair
https://support.apple.com/iphone/repair/service
Anything other than Screen or Battery will be a replacement phone and the price will depend on your warranty status.