I use resilio, which is a peer to peer storage based on BitTorrent. I don’t remember syncthing’s base protocol, but it sounds like it meets the same goals.
Resilio offers apps for my phone, NAS, Mac, pc, etc. For my phone I use selective sync for a few key folders instead of the whole thing.
These don’t get me location redundancy unless I tuck another device offsite. Most people don’t have 2 secure enough locations for this.