You could have a hardware problem. You didn't say what phone or operating system version, but maybe take it into an apple store.my phono is calling people on my contact list at random. Sometimes the phone will ring on both ends of the call. Do I have gremlins?
I have in the past, put the phone into my pocket without locking the screen and the phone will make phone calls like that. With the phone sitting on my desk or at a locked screen, I've never had those types of issues.Mine has been doing this as well. It is gremlins.