Is Windows Phone support planned?

Not happening–since there’s not enough interest in Windows Phone itself there’s not going to be support added for it specifically, and in case you haven’t seen the article here: http://www.theguardian.com/technology/2016/mar/04/microsoft-monopolise-pc-games-development-epic-games-gears-of-war
Basically the Universal Windows Platform option isn’t going to happen either because of restrictions of UWP apps.