Try this shortcut (credit to kstrike155):
https://www.icloud.com/shortcuts/2c69791fc00d4722b9bd47fc0f90d61b
1) You need to input your Client ID and Client Secret in the first two text fields. You can generate one here quickly and easily:
https://developer.spotify.com/dashboard/applications
2) Give the shortcut a custom Siri phrase, I used just "Spotify." Then you invoke Siri and say "Spotify," it will run the shortcut which immediately starts dictation. Then you just speak a command in this type of format:
Play playlist RapCaviar
Play artist The Killers
Play album Hot Fuss
Play track Mr. Brightside
(*Voice Search tip: you'll have more reliable results if you include the artist name after the album name. For example if you just say "Play album Graduation" it will likely bring you to the 6IX9INE album Graduation Day cause it's the newer/currently more popular one, but if you say something like "Play album Graduation Kanye West" it'll bring you to the correct one. Don't include the word "by" either.)
There's two main limitations:
1) The first one is a Shortcuts limitation, your phone needs to be unlocked to execute shortcuts. If you have FaceID it's just a quick glance at it to unlock.
2) The second one is a Spotify limitation - only tracks can autoplay. For albums/artists/playlists you will need to press the play button yourself.
So basically you can do everything entirely hands free except for the actual play button. Not entirely perfect, but it's pretty darn impressive and probably the best that's currently possible until Spotify adds official support for this type of thing.