I didn't know how to title this one, and it is such an esoteric thing that I figured this sub would be a good place for it... but this set of tools I think actually makes a really compelling mobile text editing/task track solution with file syncing capability naturally and easily accessible through termux's straightforward ability to add the filepath of a syncthing folder share to the termux app and thus for emacs/spacemacs and org mode.

https://termux.dev/en/

This dodges one of the biggest issues with the way sandboxing is implemented in Android by naturally connecting both your file sharing/syncing app and your text editing/task tracking app in a way that is simple and resilient to the nonsense of Android.

...but the big elephant in the room is that emacs and spacemacs are keyboard driven right.. so... how could this not be a nightmare on a smartphone????

That is where 8vim comes in! It is a really fluid and natural touchscreen keyboard that allows precise input of the core keyboard letters in a very easy but precise fashion. Somewhat unexpectedly the modal editing and space leader key command system that Spacemacs is centered around works perfectly with a touchscreen keyboard like this.

https://f-droid.org/packages/inc.flide.vi8

https://8vim.github.io/

The control input is definitely strange at first glance, but once you understand the basic way you input letters, consider a couple of basic spacemacs evil commands like "file save" "quit", "org-insert-heading", "org-narrow-to-subtree" and "widen" or any number of routine operations and most of them map out quite naturally to 8vim. Far more than you might expect given neither tool was designed for the other.

spacemacs running in termux

editing spacemacs dotfile "spc f e d"

editing and viewing an org mode file

Of course, if I am going to type a lot I use a bluetooth keyboard and transition to typing with a normal keyboard, but for simple todo list and task tracking type uses of org mode (what I almost exclusively use it for) 8vim works great.

Other essential Spacemacs keys are accessible in one tap from the main 8vim letter input screen

The reason I suggest Syncthing is that both Syncthing and Termux can so easily access the same folder locations on Android that it makes file syncing a breeze compared to how much of a silo'd corporate "somebody else's computer" headache it is for other solutions that work for Android or iOS for that matter.

https://syncthing.net/

https://f-droid.org/packages/com.github.catfriend1.syncthingandroid/

Edit I realize I didn't explicitly explain but you can install git with termux in two seconds and then just install spacemacs with git like normal.