You can simply move the photos from your phone to that home server.

That's it really.

If you want to look at them nicely, you can install nextcloud (very simple install with apache) and then mount the photos folder as read only(very simple to setup as well, just on the admin gui).

That way you'll only be viewing your images, and there would be no issues if you try another app as well.

memories is great if you're not happy with the standard photo gallery from nextcloud. This is basically the closest you'll get to say, Google Photos viewer.

Also, you can add other cool stuff like seeing your photos on the map with maps

Try it out, and if you don't like it just uninstall nextcloud. Your photos will be safe as they are just files, stored independently.