Providing all the different formats for logos for a Windows (Phone) App is not always that easy. Various sizes, even various resolutions if you want to do it right. My colleague Shinobu Takahashi created a very handy desktop tool to generate all these logos from one selected image. So you only have to make/find your artwork once and then use the tool to generate the logos and include them in your project.
Just start the tool, use Open Image to select an image from your disk. Select with the icon after the title if you want to generate for Phone or for Windows 8. Then click the square tile or wide tile on the right so you can draw a rectangle on the actual image to determine the content of that logo.
Download the tool