User can't hear incoming phone audio

One of my users found out about an hour ago that her Polycom phone was not working properly. She can hear a dial tone and the sounds of button presses when she uses it, but she is unable to receive incoming audio on a call. The volume is turned up, and the same thing happens on speakerphone calls as happens when using a handset. Other people can hear her if she makes a call and speaks. We have reseated cables on the phone and unplugged it from power, then reconnected it.