Melody Voice Assistant can now do this for you (full disclaimer: I work here). Once you start the app and connnect it to your Spotify account - you can play a song, artist, album or genre and also control your music simply using your voice.
I have an iPhone 7 plus and I tell Siri NEXT TRACK and it plays the next song. I tell her PAUSE and it pauses when you want it to play again you say RESUME. They all work with my iPhone. But it has to be those exact words or she tries to use Music app.
I was happy to see this so I downloaded the App. It works, sort of and sometimes, but not consistently. The word recognition is ok - it gets what I'm saying - but often cannot find the Spotify playlist I'm asking for or the album I'm asking for and plays some other track from some other album I've never heard of. The app needs some work before I would recommend it.