This iPhone 6 is running iOS 10.1 (14B55c), which may not be supported by this version of Xcode
Update Xcode 8.1 is now available on the app store, so you should just update your Xcode to the latest: https://itunes.apple.com/us/app/xcode/id497799835?mt=12
It looks like iOS 10.1 was released today, but not Xcode 8.1. If you upgraded your devices to 10.1, you'll need to download the Xcode 8.1 GM Seed in order to deploy to your devices running iOS 10.1.
You can download the 8.1 GM Seed here: https://developer.apple.com/download/
GM Seed's are typically the final version that gets released to the app store.