The way it works is there's a pocket surrounded by a fireplace graphic in the front of each sweater where you can slide your phone in (with a video of a yule log burning of course!). Being that they are Burger King sweaters, each also includes a graphic of a burger as well as the words, "flame grilled."
According to Ad Age, Burger King partnered with a "French hipster apparel portal," Rad.co, to produce and sell the sweaters. You can find them online here for 29.90 euros (~$31.75).
Here's a video of the ugly Christmas sweaters in action:
Photo via Burger King France.