Windows Phone 8 does not support OpenGL, as far as I know. Any kind of realistic hope would require 1) waiting until SFML uses OpenGL ES 2.0 and 2) using something like ANGLE to translate the OpenGL calls into D3D9 calls. I don't think Laurent has any plans on porting SFML to D3D9, so that's the only avenue that I see as semi-realistic. On top of that, I'm not sure how compatible other features of SFML (like audio) are with Windows Phone 8, so I'd say it's pretty unrealistic to want to use SFML for Windows Phone 8.
