There are some fantastic apps for automatic syncing of files from a mobile device to different cloud services called “Autosync for …” (previously “Dropsync”). The apps are located at https://play.google.com/store/apps/developer?id=MetaCtrl.
I would LOVE it if the Cryptomator app could copy some of those features.
In short: You create different folder pairs, one local folder on the phone and one remote folder in the cloud. Then you chose a sync method. You could, for example, start with the sync method “Upload only”, to make it simple. This would work as automatic photo uploads today, just with the user being able to choose a folder. Then you could add new sync methods later on (“Upload then delete” is a super nifty one, as you can set the files to be automatically deleted on your phone after X days).