While Sonos continue to leave Windows Phone users out in the cold there is a 3rd party option. Phonos enables you to control Sonos system from Windows Phone, you can play and pause your Sonos, select from your music collection, use the supported music services and do all the things you would expect from a Sonos app.
The app has been updated and now is fully compatible with the latest Sonos firmware (version 5.2). While the app isn’t perfect (I find it slow resuming) at least it’s option for Windows Phone users. The app costs £1.69 in the Windows Phone Store.