My understanding is that you want to synchronize local files on your phone to the cloud automatically. My advice will work only if you have a computer around constantly (laptop or desktop doesn’t matter), so don’t bother reading further if you haven’t.
You can setup file synchronization between a computer and a phone and then setup folder synchronization with a computer Mega app. This is exactly how i backup my Aegis backups to the cloud.
I personally use Syncthing for filesync between my devices. The setup may not be very straightforward, but once you do set it up it’s rather easy to use.