You need to test it because what the customer says may not necessarily be exactly what they mean.
I've had many cases where they call the earpiece speaker a microphone.
If microphone or speaker too quiet you clean the filters for them. Personally I find 99% isopropyl alcohol brushing to be the best solution, don't douse them in that of course.
If it's not working you will have to replace the part.
For earpiece not working sometimes it's the front camera ribbon assembly cable being ripped or the earpiece speaker needing replacement.
For quiet earpiece, same thing with cleaning. You will also need to open it to clean the filter on the earpiece itself as well, could also have metals stuck on the earpiece speaker which causes the issue too.
And worst case scenario is the audio chip going bad, that requires tools and experience in microsoldering to do so.