We got by just fine during the school day for decades (centuries?) before smartphones existed, and we can continue to do so without them.

Inane appeals to tradition are boring as fuck and completely useless. We should continue to circumcise infant males because we did it for decades (centuries?) and got by just fine! This says nothing about whether kids having access to cellphones is worthwhile and everything about how garbage your argument against them is.

Everybody else has a phone so the expectation is that they can do change of plans and you're supposed to know where your kid is.