Adobe stopped Flash mobile development a couple of years ago. They discontinued Flash in Android since 4.1 (Jelly Bean). And it's never been supported in iOS or WP.
The problem now is that some flash enabled websites tag IE browsers, even IE 11 in WP8.1, and force them to use flash even when they have alternate code for other browsers or OSs. I use a handy little app called UserAgent switcher
User Agent Switcher | Windows Phone Apps+Games Store (United Kingdom) which is a light-weight browser that can simulate the experience of a non-IE browser or OS. You'd be surprised how many flash-enabled sites work perfectly well in IE11 when posing as an iPad for example.