I use jellyfin as the server, then symfonium as a client on my phone. Works pretty well.

Symfonium has offline download which is handy for traveling with a spotty connection

Its fine. It's what I use when listening to music on my tv. But on my phone I use navidrome/ultrasonic. I love navidrome, ultrasonic is fine.

I am, I use Finamp as the client. It works fine, I wouldn't say its better than say Plexamp, but it works well enough as a daily driver.

Sorta, I use both Navidrome and Jellyfin. I use navidrome primarily for music listening, but then point jellyfin at the same library so that I can play music on the TV easily. With Navidrome I use feishin as my client on desktop, and I use tempo on one of my android smart phones, ultrasonic on my daily driver flip-phone (cat S22 flip), and my partner has used amperfy and subsonic on their iphone--haven't really been happy with any of the clients for iphone.

Navidrome built in webserver also works pretty ok for using at work etc. Feishin is really nice for being able to set up dynamic "smart" playlists with a gui.

I find that using something more dedicated to music like Navidrome is a little more feature built. Plus there are so many *sonic clients--so it just feels more flexible.

I still use Plexamp running parallel with Jellyfin bc it simply doesn't display all my music. I'm assuming it's a name convention thing or something but i haven't hammered it out because my library is ridiculous.

Yep