Amazon is integrated into some devices, for example Bluesound and more recent Marantz products, but I don't think there's an equivalent to Spotify Connect. My Bluesound streamer recognises and plays a version of my Amazon library in the BlueOS app, but I have to go to the Amazon Music app to edit it.
Speaking of Spotify, you say you are streaming it to your B2 from your phone. If that's right, it may not be getting you the best possible sound. Librespot allows the B2 to be recognised as a Spotify Connect device in the Spotify app. Thus the B2 streams the music direct from the internet, not via a phone. The phone only acts as a remote control and no Bluetooth connection is needed.