Laura Doel, national secretary of school leaders' union NAHT Cymru, said an outright ban would not work.
"School leaders need the flexibility and support to develop a policy that works for them to keep the children and staff in their schools and communities safe," she said in a statement.
"The fact is we live in a society where phone use is prevalent.
"But it is important that we educate children and young people, to help them understand and navigate this online world, and make sure they know how to seek help when it becomes unsafe or unhealthy, as well as clamping down on those who do not obey the rules."
Carolyn Thomas, the Labour chairwoman of the committee, said it was "a complex" topic.
"The growing body of evidence about the harms of smartphones outweighing the benefits for children is both compelling and concerning," she said.
"However, on balance we do not believe that it supports a move to a uniform ban on smartphones in all Welsh schools.
"The more evidence we heard, the clearer it became that the relationship between young people and their phones is not simple.
"There are children who experience distraction, cyber-bullying, addiction and anxiety delivered through their phones.
"There are others who are liberated by being able to manage health conditions or feel emboldened to walk to school, knowing they can always contact a parent."
In England, smartphones are not banned from schools but the UK government has issued guidance encouraging headteachers to prohibit their use.
Some Welsh schools already ban smartphones.