Actually nomophobia is more than a fear of low battery - it is a fear of being without a working mobile phone, e.g. due to loss of phone, poor signal or low battery. It is more of a psychological condition, and proper treatment is to address the root cause rather than avoid the situation - it would be like saying heroin addiction is not a problem because there are heroin dealers on every street corner.
It's almost the same thing as worrying about a car breaking down if you're 100 miles from the nearest town.
Yet we don't have a specific "fobia" for that, because it's really not a mental disorder to worry about such things.
So many things today depend on having a working mobile phone.
Boarding a train or bus, for example. You can pay using your phone, if it dies on your way and you don't have cash, that's a problem.
When you put on GPS to drive somewhere, and the phone dies midway. None has city maps anymore.
Making last minute plan changes in a group. If you don't have your phone, you won't get the latest messages.
Myself for example I've stopped carrying a debit card to withdraw money from ATMs because my banking app generates a code that I can use it.
And many others. Now I know _every single one_ of these has a work around, but most of them are "just plan ahead and have an alternative if your phone dies". After years and years of just using phones, people simply don't carry around cash or quarters for a phone call anymore.
Not to mention that I need it for 2FA.
When my phone (5X) bootlooped on a trip (before I had the hard token) and I needed to access my email for plane ticket info/etc, I couldn't 2FA into anything.. I had to remember what airline I was flying, call them, then sort out details I was relying on having on my calendar or in my email.
Legit panic as I couldn't miss work and had spent hundreds on travel arrangements. I learned my lesson and got a backup hard token (and a backup for the backup that sits in a lock box) and I should probably drop the phone based 2FA as well for just the hard token but it is very convenient.
Now, only somewhat. I generally know how to get home from where I am, and I figure if my phone were to fail, I could drive until I could find a gas station with a map. (Or perhaps a convenience store to get a charger cable or new phone.)
And of course, this fear (of being phoneless) is just an update of an old one (of being lost). It's really hard to get lost in the modern world of gps and data.
Before GPS people just carried paper maps in their cars. It's harder to find paper maps at a gas station now, but if you're preparing for a long road trip, it's not a terrible idea to just bring along a paper map to start with.
I can't even begin to list the things; everything.