There's no reason why you can't test other phones, though. If you can get friends to spend 20 minutes with you, with a promise of a nice Tesla ride as the reward, you can pair their phones to the car and do some testing, and then tell the car to forget the phone when you're done.
As for phone breakage, a good Otterbox-type case will go a long way, though personally I just pay $100 for AppleCare insurance on my iPhones, so that if I do drop it and break it it's just a small cost to have them fix it or give me a new one.