The rumored phone is expected to have Qualcomm’s high-end Snapdragon 8 Series solution, colors that match Tesla car colors, operate better as a car key for Tesla autos than any other phone, and (this is the iffy part) connect to Starlink.
There is a very high correlation between iPhone users and Tesla buyers. So, if Apple brings out a car that is highly integrated into the Apple ecosystem, it can take a substantial share from Tesla.
I think the better path would be to put the satellite connectivity into the car, which could better conceal the large antenna, and then have the phone connect through the car when a 5G network was unavailable or when you want to watch a movie (to get around data caps). Then the car gets an always-on satellite connection for remote operation and to report on attempted thefts or parking lot damage more reliably.
Last but not least, with smartphones becoming keys to cars, a Tesla phone could be further integrated with your Tesla car.