I think it is because loss of phone also means social isolation during that period.
I believe the key there is the fact that my parents made it clear why I was being grounded and spent the time explaining it to me.
Her school, extracurricular and free time with her social circle were already taken out from her and now the phone? And we all know whatever social life her friend circle has won't stop. She's just going to be left out. Once again.
I get that this is HN and a lot of people here probably didn't care to be left out (or convinced themselves they didn't).