What if the parent could handle such eventualities - based on trust in the child - with no freaking out ?
The point of this quotation is that a cell phone is a very personal thing. It's anxiety inducing and burdensome to hand over your cellphone to someone.
And that's not the mention the power dynamic between the kids with the cellphone and the kid without.
This kind of independence might be a social plus for a kid. Something like "I don't need a phone cos I can go where I want until dinnertime". No helicopter parenting.
Assuming neither, they're probably getting picked up and dropped off by a parent or other family member, with dropoff/pickup schedules arranged in advance.
It's less, "I don't need a phone cos I can go where I want until dinnertime," and more, "My mom will be driving 25 minutes to pick me up at 4PM, and my friends spontaneously decided to go bowling. I can only ask her when she gets here, but that would mean she needs to drive another hour and fifteen minutes."
I grew up before smartphones and I spoke to people around my own age. I arranged my own travel without parents checking in on me. Bullying assholes didn't need groups to amplify their message which was a good thing.
How are things better now exactly?
I'm describing how things are, not how I want things to be.
Imagine being a teenager and trying to include someone lacking a cellphone to your social group. It adds a huge amount of friction.
Including someone without a cellphone means you give up the ability to be spontaneous (assuming the kid needs to adhere to an agreed-upon schedule to be picked up by a parent), and trivial things become a literal telephone-game ordeal.
It also means almost invariably that the kid is relying on a friend's phone to communicate parents / a ride, unless that kid is so privileged as to own their own car.
Could you imagine if every time you hung out with a friend, they asked to borrow your phone, open Facebook Messenger (or whatever sensitive messaging app you use), and to contact a parent?
It also means the kid isn't included in group chats, which means they just aren't part of conversations other kids are having. You can't have a rich social life with someone you can only talk to in classes you share and for 20 minutes during lunch break.
The "green bubble" phenomenon is bad enough as it is. I don't like it, but for all practical reasons, owning a cellphone is necessary for a kids social life in the United States.