Just to be clear - if you call someone, they cannot hear you but you can hear them just fine, right? What happens if someone calls you instead - the same thing?
Next, you make it sound like at one point the problem was fixed, and then it started happening again. What was the fix?
Finally, from within the Phone app, have you unchecked Call settings -> Additional settings -> Noise reduction?
Sent from my rooted, debloated, deodexed Sinclair ZX-80 running CM -0.001 using Tapatalk 4
I have seen this in other forums. Their problem turned out to be trash/dust bunnies in the mic hole at the bottom of the phone.