Set Spotify as Default Music app on iOS 14.5 Beta
Apple is testing out the iOS 14.5 update and currently available as Beta. It packs an interesting feature to set any Music Player as default player.
As you know the iOS 14.5 is still in Beta and can take some time for its public release. So make sure to update your iPhone to iOS 14.5 Beta to enjoy this feature.
If Spotify is your favorite Music Player, then you finally get to set it default Player on your iPhone. Since its still Beta it may not be stable.
It is possible with the help of Siri. So, launch the Siri and ask to play a song or artist. In future updates, the process can change. But for now voice assistance works.
Once you ask Siri to play any song, it will pop up a menu with the list of available Players including Spotify.
From the menu select the Spotify app and it will start playing the Song. It will not ask to choose the app next time when you ask to play a song.
Here's how it works in Video from a Source.
You can try this process to setup other music player as default on your iPhone. This may not work at the first time, so try it multiple times or even by changing your play request.
We may see the option to choose any Music Player as default with reliable method in future update. But for now you can try this method to enjoy Music on your iPhone.