I suspect that it's an app that you have installed. This was happening to my phone a few months ago, right after iOS 10 was installed, after I installed the weather app Dark Sky. As soon as I uninstalled the app, the restarts stopped (it was, at the time, the last app I had installed, and no there apps had been updated since the reboots started happening, so it was easy to start with that app). My phone didn't restart as regularly as yours did, but it was happening often. I'd been using the iOS 10 beta for a month before I installed Dark Sky, so I was fairly certain it wasn't just an issue with the update.
I'm not suggesting that it is Dark Sky, but I'm guessing that you have a misbehaving app?
02-02-2017 12:05 PM