I think using a phone is less of a problem than it's made out to be, myself. Laws against that, outright speed limits on open highways and the requirement to come to a dead stop and stop signs I don't agree with. Please don't ask why I don't agree with the latter...
But not wearing a belt is an imposition on others if you're injured in an accident because you didn't have on on. Somebody has to pay your medical bills, after all. And somebody has to tend you, visit you in hospital, take care of your affairs or your job.
Let's face it, they are instrumental in saving thousands of lives around the world every week. Why not encourage yours to be one of them?
