The phone as key was introduced to the model X with the refresh in 2021. Prior to that, it was the key fob. There is no way to retrofit the legacy model X’s to the passive phone as key. However, all versions of Teslas let you access the car via the app on your phone, which lets you not only unlock it but also drive it. This requires the car to have a WiFi or cell signal. Phone as key uses Bluetooth.