My iPhone 4s is making a receiving phantom calls

My iPhone 4S is making a receiving phantom calls. It is updated and been synced recently. It was happening to my boss and myself. I got a call from her that was not in her log, and she received one from me, not in my log. It also happened with our IT person who came by yesterday. Also, sometimes my phone will not ring when it should and it goes straight to voice mail. Since I am the common denominator then I figure it has to do with my phone. Someone please help!