The mic down by your charge port is dead. There are two, unless I'm confusing myself again. The one that operates while using the speakerphone mode is up top near the earpiece. Unfortunately, I think everything is on one board in these phones, so this is not a part that can just be swapped out. I would go back to your service provider and explain what's going on. That there is no physical damage makes it probable that this is a manufacturer's defect.