The iPhone 8 doesn’t have a signature failure with the Audio IC but it is indeed possible. However, it could also be just discreet microphone issues.
There are 3 microphones in the iPhone.
https://support.apple.com/en-us/HT203792
* The bottom microphone is for Voice Memo and phone calls.
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* The (top) front microphone is used for FaceTime calls, Siri and selfie videos with the front camera (FCAM).
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* The (top) back microphone is used for videos with the rear camera (RCAM).
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Make sure you update your device to the latest version of iOS and then try to isolate which microphone is not working properly by trying each individual microphone with the related apps above. Check the microphone port holes for dust and debris which could be attenuating the sound.
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* The (top) front microphone is used for FaceTime calls, Siri and selfie videos with the front camera (FCAM).
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* The (top) back microphone is used for videos with the rear camera (RCAM).
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If the issue affects more than one microphone, then it could be the Audio Codec IC on the logic board. Anything at the logic board level will require micro-soldering so you would need to find a repair shop that offers those services.
Has something happened to the phone prior to these issues appearing, such as a drop, repair attempt or contact with water?
The iPhone 8 doesn’t have a signature failure with the Audio IC but it is indeed possible. However, it could also be just discreet microphone issues.
There are 3 microphones in the iPhone.
https://support.apple.com/en-us/HT203792
* The bottom microphone is for Voice Memo and phone calls.
* The (top) front microphone is used for FaceTime calls, Siri and selfie videos with the front camera (FCAM).
* The (top) back microphone is used for videos with the rear camera (RCAM).
Has something happened to the phone prior to these issues appearing, such as a drop, repair attempt or contact with water?