The way I do it is search for the media on my phone using the Jellyfin app, and the app has an option to cast it to whatever detected device via DLNA. You can

The way I do it is search for the media on my phone using the Jellyfin app, and the app has an option to cast it to whatever detected device via DLNA. You can do this from the phone app or web browser on your LAN. You do have to have your media metadata correct though, e.g. ID3 tags, etc.