If you really want to be fancy, you can deploy a script to watch files for changes and do rsync immediately when it happene.
I use a tool that does that, it's called Syncthing.
Plus, rsync -a never deletes files.
syncthing is bidirectional, syncing changes in either direction, and supports syncing any number of clients, not just two.
Watching and syncing immediately - yes, that's what syncthing does. Why reinvent it with something worse?
FTP is not encrypted. Unless you use SFTP maybe. (I wrote an SFTP and FTP-over-SSH client in Visual Basic like 20 yesrs ago lol).
And even then, you miss out on all the optimizations with prolly trees and other goodness that rsync has.
No, sorry, that solution sucks. CVS? That’s super outdated.
Anyways, if you're at the grocery store and you need to see your shopping list, and you're happy with your current workflow of opening up Termux and typing `rsync -avrsomgwtfbbq me@server/shopping-list.txt` with your thumbs, then by all means keep doing that! For the rest of us, there's Syncthing.
SyncThing doesnt actually have an iOS client that syncs reliably. I tried some, when I was test driving it and Resilio Sync and others.
https://forum.syncthing.net/t/syncthing-for-ios/16045
On your phone you’d probably just visit a website, and access your server via HTTP.