In some hands, empowering, in other hands, a weapon. It's less about smartphones specifically and more an abstraction for the internet itself. Take the internet away and it removes the metaphysical vector for exploitative outreach to children.
It would make it very difficult to produce new CSAM if you eliminate the channels over which children are discreetly coerced into running away or producing it themselves.
I lived through the 70s. Worked at the BBC for a while. Nonces (kiddy
fiddlers) are a social psychiatric problem. Policing networks or
endpoints is treating the symptoms.
Nonetheless I agree the utility that children get from access to the
mainstream "Five Giant Enshitified Websites" doesn't really surmount
the damage done. The main harm, in my opinion, is simply to general
mental health and wellbeing. So that just adds to the case for an age
restriction for smartphones. If that reduces potential contact with
nonces then all-good, but the reality is that child abuse happens by
people IRL, usually trusted family or neighbours.
Maybe the tide is turning and we're "getting there", and that's why I
defended and supported many parts of the UK Online Safety Bill - even
though other parts of it are trash. However this focus on CSAM to push
unworkable restrictions is the usual dishonest politics and posturing.
We have more general problems with minors and the Internet, and most
of them are "live rail" issues the media and politicians won't touch.