Key word is access. Not everything on your phone is available to the vehicle, but if, for instance, you allow your car to access your contacts, it downloads all of them with all the metadata which the company can then sell. Or internally run through algorithms to profile you and everyone who uses your vehicle. If you use Android Auto or CarPlay, or just connect to the entertainment systems, they’ll skim whatever metadata they can and phone it home. Even worse if you use a car’s official app, it will use your own phone as the transmission point.
No, it doesn’t immediately transmit an entire backup of your phone over a personal Bluetooth connection, but I was very precise in how I worded my sentence.