Phase One makes a "Flex Adapter". I have been using it on a Sinar P2 with a P-45+.
It works well if you have the right lenses. It also allows stitching images together for larger files. You can get plates for any Mount of Phase one back. Kapture Group also makes sliding back adapters.
It is nice to be able to go back and forth between the view camera and medium format system as needed.
My only caveat, is the P2 movements don't work as precisely with the smaller digital chips as they seemed to, with 4x5 film
As someone else pointed out, the Phase backs don't work with the Hy6 and it has been talked about quite a bit.