Suggest to the dealer that he look in the VW electonic parts catalog, at the illustration that shows the air filter plenum. The snow screen will be illustrated there. VW parts catalogs are identical all over the world - even if you took the car to a VW dealer in the middle of the Sahara desert, or in Death Valley, CA, they would see the snow screen on their parts catalog display.
In the meantime, here is a picture of a snow screen from a W12. The part number is visible (upside down) in the middle. This should help the dealer get close to the part number of a snow screen for a Phaeton with your engine type in it.