Yes you would need the Wireguard app on your phone, and certainly for me it works beautifully (I use Android - I can't speak for the iOS app but there is one).

Yes you would need the Wireguard app on your phone, and certainly for me it works beautifully (I use Android - I can't speak for the iOS app but there is one). I don't actually remotely host Jellyfin, but I do use a range of other things like Bitwarden, Nextcloud, Dovecot/Postfix, and some small web apps, and it's really smooth. The only public port on the server is the VPN.