If you want to access your notes and todo-lists from several computers and your mobile phone then there are several tools you can use. As EasyOrg is based on plain text files there is great flexibility and you do not need to rely on any built in syncing.
One of the most flexible and transparent tools is Syncthing. You can set it up to sync specific files and/or folders and once done they will be kept in sync if you update the files on your computer or on your mobile. Syncthing does not store anything in the cloud.
In this documentation we will not go through how to set it up as it is well explained on Syncthings website.
Another great benefit of using text files is that you can get versioning support. You can go back and forth in time to refer to older versions of your Org files.
EasyOrg supports this out of the box as an integrated solution. Go to 'File > File History' in the menu. You will see all saved version of the current file including a diff view. The diff view compares the old file with the current version in the editor. You can also see a full view of the old file. And you can copy parts or all of the file if you like. See more about this feature on the EasyOrg Features page.
If you prefer to handle versioning outside of EasyOrg that's of course also possible as hte data are stored as text files on your disk.
Syncthing, Dropbox and pCloud all support file versioning in case you store your files on a disk handled by them. Another obvious tool for file versioning is Git.
Thanks to using text files as storage medium it's easy to setup a backup to run every day and store it on another disk or server. You probably already have a backup solution in place and if your Org files are stored within a directory that is backed up, you already have you EasyOrg files backed up!
Other alternatives for sync could be using GitHub, WebDAV, NextCloud, NAS or other cloud storage services.