I designed this Nerf Phoenix LTX battery cover to replace one that was missing on a used tagger I purchased. This battery cover should fit just as well as the original cover. It requires two M3 8mm screws to hold it to the Phoenix. The lower part of the screw hole is intentionally a little snug so when the screws are backed out, they can stay in the cover without falling out.
I printed this battery cover on its side with PLA and using an adhesion plate. The top side of the cover comes out near perfect while the bottom side needs some clean up because of the supports to look good. Once it is printed, make sure all the small support pieces are cleared off where it touches the gun. If not, it may not slip on like it is suppose to, but it will indeed fit when they are clean. If you print this and it works for you, please let me know in the comments.