Because of the current library restrictions for Unity on Windows Phone / Windows Store, building to those platforms is currently not possible (see the FAQ).
However, Unity's roadmap indicates that Unity 5.3 may make it finally possible, so while I can't promise anything there is at least some hope with this.
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However, Unity's roadmap indicates that Unity 5.3 may make it finally possible, so while I can't promise anything there is at least some hope with this.