Banning phones in schools should be a decision for head teachers and not "imposed nationally by the government", England's children's commissioner has said.
Nine in ten secondary schools restrict the use of smartphones, according to a survey of 19,000 schools and colleges commissioned by Dame Rachel de Souza.
Dame Rachel said children were racking up hours of screen time at home instead, and that "the people with the real power here are the parents".
Her comments come as the general secretary of the UK's largest teaching union said a government ban on phones would "take the pressure off schools".
Dame Rachel told BBC Radio 5Live that the vast majority schools were already restricting and banning phones, adding: "Blanket ban if you want, but they're doing it."
The former head teacher cast doubt on how effective a ban would be on those schools without strict policies, noting that the government can impose rules but "unless a headteacher really believes it, they won't do it properly".
A minority of schools want a ban because they are "worried about parents" not supporting the decision, she said.
"That's why I'm saying parents, 'get behind your school'."
Dame Rachel told BBC Breakfast that "parents have to remember they are not the friends of their children" but are "there to protect their children [and] put the boundaries around them."
