My iPhone6 is having the weirdest problem: I can't be heard on phone calls, whether incoming or outgoing. I can hear the other person. I can be heard on FaceTime audio calls and Skype calls, and can record voice memos fine. I spent several hours at the Apple Store last week and they were baffled. Any ideas what might be wrong? It's super frustrating! Running the current iOS; restoring to factory settings didn't work.