iPhone pocket dialing while locked
Tonight something unusual happened with my iPhone SE. During my break at work, I checked my phone for text messages and weather; nothing new. I put it to sleep via the sleep/wake button as I always do. Passcode is set to be required immediately.
Approximately 15 minutes after I stopped using my phone (according to the time stamps), it began dialing the two numbers in my recent calls list. The outgoing calls lasted between 3 to 7 minutes for a total of 13 calls over a period of 1.5 hours before I first started hearing a music-like sound coming from my phone. I presume the music was coming from the other end of the call. The recent callers were an automated system from my work and an unknown spam caller.
I took my phone from my pocket; it was sleeping and locked. I woke it up with the home button and entered my passcode. The sound stopped. The window visible in the foreground was the voicemail greetings settings where you can choose a new greeting message.
How could this happen while my phone is sleeping and locked? How can I prevent it from happening again?
Additional details:
Using the latest software 10.2.1
Siri is disabled
Not jailbroken
iPhone SE, iOS 10.2.1, null