The phone app does not use Bluetooth. It communicates with the Fremont servers. And then your car is connected to Fremont. If the Fremont Tesla servers are down, then you are out of luck using the phone app to unlock your car or for that matter any app functions. For Model S/X the key fob will still work and for Models 3/Y the key card will still work. They communicate independently with the vehicle; not using Bluetooth.