If you are asking about the current plastic Empire Griffon I'm guess that would be a no. They would be too small looking at those pictures. They may be just the right size for the Isle of Blood Griffon though.
The phoenix is a lot bigger than you think it is. The model is the same width as the Imperial Griffon, but the Imperial Griffon has thicker, wider wings, which are bent, and fully stretched out would be an inch or so wider each side. I think you could get away with the phoenix wings on the Imperial Griffon, because they're only a little bit smaller, and also because the current wings on the Imperial Griffon actually look too big.
The problem would be how well they fit at the joint to the body of the Griffon, and how much greenstuffing of feathers around that you would have to do.
The phoenix is almost twice the width of the Isle of Blood griffon, so the wings would look way too big on that.