Hello friends. Its very simple. Don't stress alot about it. Just take a safety pin and gently clear the ear piece holes. I did the same now and was surprised that the voice is clear now.
Try this on the first priority then go with software etc.
Your speaker is probably dirty. This was my problem. Use tape. Rub it over the speaker really well then pull off. Do this a few times. The stronger the tape the better it should work. I used duct tape. My friend used scotch tape. But they both worked.
I tried every fix I could find on every site. I ended up having to file an insurance claim with Assurion and getting a replacement phone. I think that the factory/device warranties on these phones should be extended. It is ridiculous that I had to pay for a replacement phone when the issue was with the equipment, with no mishandling or misuse on my part.
Annoying, but not as annoying as not being able to take a phone call without earphones or speaker.