Q: I am unable to hear the phone when I call someone and they can't hear me.

I am unable to hear the phone when I call someone and they can't hear me. I can't hear the ring tone out, but I can hear my phone ring for an incoming call. They can't hear me speak when I answer. There is a microphone icon that has a slash through it, so I assume the phone has been muted somehow. Touching the microphone, won't unmute it. How can I restore normal function and avoid doing this again?