Immich has a setting that does automatic photo backup over WiFi, I use the android app as a Google photos replacement. You can choose however many folders on your phone as you want (I just do camera roll) and enable only backup over WiFi and it backs up all the photos in original quality. I self-host the server on my Synology with a reverse proxy (can’t forward ports at my current place due to cgnat) so I can access it from anywhere.

I believe the app is cross platform so the iPhone version should be identical to the android one.

Woah federation would be huge!

Someday I would love to be able to share and receive shared photos / albums to and from users on different servers. Especially if it lets me sync the original files so that I can keep a copy in case their server goes down. It would also be neat if you could enable activitypub so that your account could show up as a fediverse user that people can follow for public or approved follower only posts, pixelfed compatibility would be super cool.