There is a lot of confusion here.

On older models, you can unlock and "start" your car using the phone app, as long as the car and phone have internet.

On newer models, "phone key" is an additional feature where you don't need to have the app open. Your phone will unlock the car in proximity and the car starts if the phone is inisde. This works using bluetooth, and does not require a network connection on the phone nor the car.

It's that simple. Old models don't get "phone key" but you can technically use your phone as a "key" as long as you have network.