There is a new way to mirror your Windows Phone screen on your TV, if you have either a Roku 3 or a Roku Streaming Stick. The procedure is very simple. All you have to do is enable mirroring on your phone, and then pair it with either the Roku 3 or the Roku Streaming Stick. After you do this, everything on your mobile device’s screen will also show up on your TV. You can read the full guide here.
Since it is with Roku, a company that already helps you stream media to your TV, the emphasis is not on mirroring TV (e.g. Netflix) off your phone. This is meant for you to share things such as documents, Facebook videos, or media you made and want to share on a bigger screen. Roku sees it as a way to share content on a bigger screen in your living room and in a conference room.
Also note that it only works with compatible phones (see the list here), and the feature is currently a beta.