Everyone is different, but I am sure there are some folks who can and will plan out their whole vacation, including FP+ and stick to it.
Furthermore, a person could easily change their FP+ in the evening in their hotel room for the next day. I did that a little in Dec during our trip -- I would tweek things. Mostly, I stuck to the FP+ reservations I had booked 2 months before the vacation, but I did do some changes based on what we had already done during the vacation.
Anyway, being "forced" to carry your phone strikes me as one of those complaints brought up specifically to complain. Personally, I would say, if you want to go that vein, that mentioning that a lot of people simply don't have smart phones (or cell phones at all) is a much more valid point. That actually would impact a lot of guests.
Are there people who don't want to carry a phone on vacation? Sure, but I'd imagine they are an exceedingly small percentage of WDW guests. The vast majority carry and use phones in the parks and for most people having to get on the phone once or twice a day to change a ride time is a small burden in the grand scheme of park planning.
Seriously, it's grasping at straws. There are a ton of legit complains about FP+ that affect a lot of people (the limit of 3 per day, one park, tiering) plus plenty of technical aspects that are issues (MBs not working, glitchy system that sometimes does or does not work to reserve/change FP+, etc.) or global issues (having to reserve ahead of time/lack of spontaneity, potential for FP+ to be out for a ride you want, longer standby lines on rides that added FP+) that complaining about minute issues that most people wouldn't care about only undermines your case.