Hi,
I may have an alternate solution for you.
It requires that you have a 24x7 PC running Windows or Linux serving your files from Microsoft. When configured it gives you the option to use webdav with ssl to connect to your Microsoft OneDrive.
I can write up a set of basic overview instructions if you like?
In a nutshell you use apps called rclone and caddy and ddns to give you a valid domain name that can get a SSL certificate that Caddy will acquire for you.
Rclone gets the files from Microsoft using standard Microsoft Authentication. Then it serves them using webdav.
Then caddy gets the cert for your ddns name.
Joplin uses webdav to connect to your domain.
It sounds a little bit quirky but it should work. I have set it up almost all the way I just need to add it to Joplin to confirm that it works. Let me know and I will test it this evening.
I happen to have a router that supports Dynamic DNS automatically. It gives me an Internet routable domain name that can be registered for an SSL certificate.
You can do the same thing without a router as long as you run ddns to give you a routable domain name to your cable modem at home I presume?
You'll be using an internet routable domain name so your phone can be at home or away it doesn't matter. What matters is that you be able to forward ports 80 and 443 from the router to the PC that you designate to share the files. You can actually use different port numbers if you wish.
Using this setup in case anybody else is reading this enables you to locate your Joplin database files on any cloud provider that rclone supports and there are over 50 of them. Rclone will be responsible for opening a connection to OneDrive for files access and also serving the files to all your devices.
UPDATE
I set this up completely and tested it and it works.
Using webdav you can connect to any one of the more than 50 Cloud providers supported by Rclone.
Yes, Joplin via webdav can access any server or cloud server Rclone can mount.
User ID and password supported. Ssl end-to-end encryption.