Schools in England would be forced to ban mobile phones under government plans.
Department for Education (DfE) guidance already says phones shouldn't be allowed, but head teachers are able to ignore it if they disagree.
An amendment to the Children's Wellbeing and Schools Bill now proposes making it a legal requirement.
Many teachers have long voiced concerns that smartphones distract pupils and can add to problems such as bullying.
"We have been consistently clear that mobile phones have no place in schools, and the majority already prohibit them," said a DfE spokesperson.
"This amendment makes existing guidance statutory, giving legal force to what schools are already doing in practice."
On Monday, the House of Lords voted by a majority of 107 to ban phones during the school day.
The proposal, by Conservative shadow education minister Baroness Barran, includes a potential exception for sixth-formers, medical devices and some boarding school settings.
The House of Commons is now expected to vote on the amendment on Wednesday.
The NASUWT union previously said it supported a statutory ban, while headteachers' union the NAHT also backs it.
NAHT general secretary Paul Whiteman said it would give "clarity" and "remove any ambiguity or differences between how schools approach smartphone policies".
"Schools will only then need to decide how to implement and enforce a ban across their school community and the government must provide any support they require to do so effectively," added Mr Whiteman.
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Skills minister Baroness Smith of Malvern said the government had listened to parliament and "to concerns about how we support headteachers in delivering on this policy".
However Laura Trott, the shadow education secretary, painted it as a win for the Conservatives.
"I am delighted we have forced Labour to see sense and U-turn," she said. "This is fantastic news for headteachers, parents and pupils across the country."
The change comes as concerns grow over children's use of social media.
A process that could result in an Australia-style ban on social media for under-16s began last month as the British government began consulting the public on how they want young people to be protected online.
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