Earpiece Not Working But proximity sensor does

As stated in the earpiece repair guide:

This assembly is paired to your individual iPhone from the factory, so you must transfer it from your old display to your new one during any display replacement.

The flood illuminator forms part of the biometric Face ID security feature, and Face ID functions will fail if the original component is damaged or incorrectly installed. Replacing it with a new part will also cause Face ID to fail, so take extra care not to damage any of these components during this procedure. If damaged, only Apple can restore Face ID function.

So this means if you replace the front sensor/earpiece assembly with the flex cable you’ll lose Face ID. It is possible to replace the speaker alone, but this requires high level of soldering skill as can be seen in this video of NorthridgeFix: https://www.youtube.com/watch?v=qo-tOq8y...