If the caller can't hear me, is it an earpiece problem?

As I was speaking to someone on the phone, they weren't able to hear me mid-conversation anymore, but I was still able to hear them clearly. I checked to see if I may have pressed the mute button, but that wasn't the case. The speaker and sound works perfectly fine with other applications such as voice memo, just not when it comes to calling. A few days later, when someone called, a crackling/static noise started to appear. Does anyone know how I can fix this?

I went to to the apple store to see if they could help. All they did was take a led flashlight, looked at the part where you insert the charger in, and said that there has been some water damage and that the only thing I could do is replace the whole phone itself -.-