Windows Phone & Windows RT
At the moment there is no Anki client for Windows Phone or Windows RT. Due to limited resources, a client for these platforms is not expected in the near future. In the mean time, you can still use Anki via AnkiWeb, and Anki will work on the Windows Surface Pro.
Windows Phone's Internet Explorer has a bug where it renders AnkiWeb smaller than other mobile browsers. If you install Chrome on your Windows Phone device and access AnkiWeb through that, the interface should be more usable.