Currently I'm using Jellyfin (since I already use it for other stuff), but it isn't ideal. No option to download entire albums easily, and if the server is offline then I can't even use the music downloaded to my phone.
I use Owntone server and various airplay devices around the home. That way I can just use the built in Apple Remote and streaming from iOS devices. I think there is similar apps for iPhone or you can use the web ui of Owntone.