Falling off your bike and cracking your head open or breaking something or whatever. I used to bike through somewhere where not a lot of people would pass by.
Or even worse, get hit by a tractor who didn't see you and not be found until later, which can cause permanent damage. Happened to somebody I know sadly, she is disabled for life now. Yes, the person in the tractor should have been more careful and have seen her, but you can hit somebody with one of those and not notice it.
I also never said they should use the phone to call the parents, you can also call 112 with those.