Spotify beta tests the ability to use Siri to control its app on iOS 13
The wait might not be too long until you can ask Siri to play music for you on Spotify. The streaming service is beta testing integration with iOS 13's SiriKit audio APIs, which will allow you to ask Siri to interact with the app.
What the API will allow iOS users to do includes everything from playing artists or albums as well as theoretically manage playlists, like tracks, etc. The caveat is you will need to instruct Siri that you want the action done on Spotify, so the virtual assistant knows you want it to interact with this specific app.