During phone call I can only be heard in speaker phone mode.
When I am using the phone to make or receive a call I can only be heard when I put the phone in speaker mode. I can hear the person on the other end fine with the phone to my ear or in speaker mode. It has never been in contact with any liquids nor has it taken any big drops or hits. I have already replaced the speaker assembly and that did absolutely nothing. I've tried cycling the speaker mode on and off during a call and applied pressure to various spots around the edges, to the front and back. Am I looking at a logic board problem or an issue with the ambient noise dampening microphone? Thanks in advance for any and all feedback!
There are two possible reasons for why your phone isn't picking up your voice.
1. You are having a software issue. Since you said you never dropped it or had it come into contact with water, there is a possibility that you just need to do a software restore and it may fix the issue.
2. The bottom microphone isn't working. The microphone at the top seems to take over for picking up your voice when you go to speaker phone. Try disassembling the phone and reseating the connector which is right next to the battery which has a metal plate being held down by two screws. If reseating the ribbon doesn't fix it, then the microphone needs to be replaced. The microphone is attached to the dock connector so it will all be replaced in one component.
There is a third possibility which is a malfunctioning headphone jack, but since you stated that you can hear from the earpiece while on a call, then that tells me that you are not having the headphone jack issue that I suspected.