Stolen iphone
How do I put a message on the Lock screen of a locked stolen phone?
iPhone 6s Plus
If your iPhone, iPad, or iPod touch is lost or stolen - Apple Support
Turn on Lost Mode. Using Lost Mode, you can remotely lock your device with a passcode, display a custom message with your phone number on your missing device's Lock screen, and keep track of your device's location. If you added credit or debit cards to Apple Pay, the ability to make payments using Apple Pay on the device will be suspended when you put your device in Lost Mode.