In the newest version of the Spotify Desktop app you can control your desktop app from your phone or tablet (Android or IOS) using Spotify Connect. You can even change the volume, so that’s pretty cool! When you use the Beta version of the Desktop app you can also control any Android device from the desktop app, so it’s now both directions. A downside is that volume control doesn’t work when controlling an Android device from the Beta Desktop app. Let’s hope that feature will be added soon 🙂
It seems to be that Spotify is on it’s way to make Spotify Connect available from and to any device, including volume control, which is great I think!