9 year old refuses to wipe, help?

Heyy, I need a little bit of help from parents or anvone who knows about caretaking behaviour :(. So I'm an older sister and my younger brother completely refuses to wipe. My parents refuse to either teach him or do it for himself to the point he WILL sit in the bathroom for hours on his phone waiting for someone to come and do it for him. Plus, our parents keep saying it's my responsability to teach him...and I've tried, though he just goes completely mute and stares at me like I've personally offended him before throwing a tantrum and crying,.

I know that as a family member it is my job to help but this is getting ridiculous. Our parents keep pushing their responsabilities about my younger brother onto me and I don't know what to do, because I have tried and it leads us all nowhere.