Retheme as a horror movie where THE CALL IS COMING FROM INSIDE THE HOUSE!!!
Scenario: You are a babysitter and there is a psycho chasing you down! You got separated from the kids you were sitting and need to find them without getting killed yourself. Multiple "endings" with you saving yourself, others or everyone getting wacked! The phone integration could be the way you get info on where to shoot (or not shoot).
Moreover, your phone will be set to vibrate and not ring annoyingly. Or in a fit of strategy, you could turn on a "ringer" to distract the killer.
I only gave this idea 10 minutes of thought, but playing an intelligent female protagonist trying to save herself and others would be a very compelling narrative.