It can be multiple people's fault. If he knows it will upset his parents to not be able to call him, and at this point clearly knows that they're going to bother his friends instead, that's still a decision he's making. He could tell his friends to just block the number/ignore it, or talk to his parents about not contacting him. Sure, if his mom is stalking him and harassing his friends, that's her fault/problem, but that doesn't mean it's not a burden on his friends. I'd be more sympathetic for sure towards his situation then.

I live tens of hours away from my parents right now. Calling them is how I get/keep in touch with them. If I decided to get rid of my phone, I'd be sure to come to some sort of other solution that would be acceptable to them and not just cut them off.

The issue is he presumably knows that his parents are like this and want to stay in touch with him. If he can't convince them to use email/skype/whatever else, then that's his issue to manage. He's not entitled to push that off onto his friends just because his parents are unreasonable. Either deal with your parents unreasonable demands by having a basic burner phone, or tell all your friends to just not pick up/blacklist it.

To me, is like if you decided you were worried about the environment and started biking everywhere. I can respect that as a decision, but it doesn't mean it's not imposing on me to always be showing up to things late because you haven't adjusted to how long it takes to bike places.