Since Adobe aren't remotely interested in Windows Phone users, how can I get patterns into the pattern library without using the Adobe Sketch app?
I may be mistaken, but I believe the app you're referring to is Capture CC. That's the mobile app that enables the creation of brushes, color themes, shapes, and patterns and places them in libraries that can be used in our desktop (and mobile) applications.
Since that app isn't available for Windows phones, the only way you could get patterns into a library would be to have someone share a library (with patterns in it) with you. You'd be able to copy it to your own library. Patterns are currently only usable in Photoshop CC.
Hope that helps.