Entity Id error

I am getting an error with my configuration. I am trying to set it up so everyone shows whether they are home or away. I have an issue with my wifes iphone not showing up on my router so I am having to manually add it but when I do I get this error. If I dont add it, I cant see whether she is home or away. Any help is appreciated.

Entity id already exists - ignoring: device_tracker.iphone. Platform mobile_app does not generate unique IDs