Why is there a small hole on the rear camera of a smartphone?

The small hole on the rear camera is a noise cancellation microphone. It is a key part of the phone’s audio system, not a defect or camera part.
For your reference, here are more details about the microphone:
1. It works with the main microphone to cancel out background noise during calls or recordings;
2. When recording video with the rear camera, this microphone captures clear directional audio from the environment. It helps deliver stereo or spatial sound for better realism