A screen saver is a program that changes static images to prevent burn in.
you are talking about the "desktop or background".
Now to your question.... yes you can use an image from your phone, but it has to be the correct aspect ratio (800 x 384) and smaller than 1.5 mb in size. The image must be on a usb memory device or a memory card in the map reader.
And only can be done with the 2015. The 2016, sporting SYNC 3, does not permit changing the screen desktop. Not a real problem, as the Chrome Pony looks pretty cool.