I used to carry a legit dumbphone (not one of the new Android/AOSP “dumbphones”) and that worked just as well. It’s even trendy now!
It is entirely optional.
This doesn't mean much. I know multiple people who fit this description, live in the US, and can't speak or read English. However, speaking English isn't meaningfully optional. You will face constant limitations and problems in every aspect of life. There are people who don't use electricity, so I guess by your definition that's optional too?
> I never think about not having one.
Sure you don't.
Seems very country / region specific?
Except it really isn't, it just seems that way when you spend a bunch of time on your phone. As part of an utterly graceless transition to middle age I bailed on social media and have aggressively refused to engage with service-related apps of any kind (fuck mychart, drive-thru mobile apps, and the horse they rode in on). To the extent that I use my phone at all these days it's to check text messages, field calls, and (rarely) navigate via maps. I've reverted to the Old Ways (mailing paper checks, calling ahead to get live humans to explain shit, etc) and it's been pretty frictionless. I've yet to encounter a situation where I was prevented from doing anything because I didn't phone.
Actually compared to signing in to a website, 2FA, dismissing the popups to explore new features, entering payment info, then confirming---writing a check and putting it in an envelope takes less time.