sensors, camera, front mic working perfectly expect ear piece not work

Is this following a repair or a heavy impact or did it just occur naturally?

First I would take a look at the earpiece speaker grill, the mesh you can see in the cutout of the screen. It may be very dirty with lint and dust causing less sound to get through. You could clean it with isopropyl alcohol and a cotton swab. If that doesn't solve your problem, I would open up the phone (follow this guide) to see if it is properly lined up with the contacts. You can also clean those contacts with alcohol.

If everything looks clean and well aligned, then you may have a defective earpiece speaker.