"The phone is, IMO going to be a bit too small. That's my plan eventually anyways."
Agree. I think the phone is fine for occasional use, but suspect that many will find it harder to see the app than on a tablet. I know people are suggesting using older cell phones that are not currently used for data/text/voice, but this has potential for disappointment as apps are modified over time.
My own preference is to use Apple devices, both out of habit since 1984, seamless integration with my desktop/laptop, and because the result of Apple's monopoly and its expense is that you have one, uniformly functioning system. At the risk of angering some Android enthusiasts, the implementation of some things in Android apps seems to vary from manufacturer to manufacturer and that occasionally renders apps quirkier on occasion (second hand information, not personal experience). But one can always get an inexpensive Android tablet or phone if that's what you prefer and test it out. Personally, I'm a handheld remote fan, so I'll continue to use my cab-1 (TMCC), my LionChief remotes and Universal Remote, and my newly acquired (before the recent gold rush) cab-2s. For belt and suspenders will also get a cab-1L.
At the risk of being repetitive, if you have TMCC (the original 1996 cab-1/command base), you don't need anything else to control any Legacy engine ever made. Some functions are not available, but nothing critical to most people. If you have only recent Legacy locos (apparently 2018 going forward) with Bluetooth on the box, you can use the free app or the 50 buck Universal Remote. No command base needed.
I'm guessing that most people who have been in the hobby before 2018 and prefer command control for Lionel locos have something that is currently working (TMCC or Legacy system). I had only TMCC, but decided to obtain the Legacy system since it's going away and I do have some Legacy locos. Paid about $100-150 more than the best previous price for these, but cannot blame Lionel for that 
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