Problems with making calls.

About two weeks ago, I started having a problem where I couldn't hear the person on the other end of the line when I made a call, but they could hear me perfectly fine.

Yesterday I managed to find what triggers this. The light sensors that turn off the screen when you've got the phone against your face also cut off the speaker. When the phone is away from my face and the screen is on, I can hear the other person normally. However, as soon as I put the phone next to my face or block the light sensors, the volume is cut off. Putting the phone on speaker makes this issue go away, but is inconvenient when you want privacy.

The easiest way to fix this would be to disable the light sensors, but I'm not sure how to do this, or if it's possible at all.

I've tried searching for a solution, but all I've found were posts on increasing the call volume. Anyone know what's wrong or how to fix it?

Yesterday, covering up the light sensors with my fingers would consistently disable the audio (only when speakerphone was off). Today I've been getting mixed results. I'll try some more troubleshooting tomorrow and will report it here accordingly.