The phantom was designed to fit in a filco case but a QFR case can also be modified so it will fit. Sadly no one has came out with good phantom cases lately, there have been a few failed attempts along the way but nothing consistent.
Some people use a makeshift cardboard case and you might be able to get some acrylic and use some spacers to make a makeshift bottom to screw it into somehow, but IIRC holes for screws in the phantom itself are limited.