AbramsPT,
That’s an interesting idea! I’m not sure it’s something I’d try, though.
You could change the color of the armor and dub new lines (although getting it perfect might take a long time), but you still have Gwendoline Christie’s stature and movement. I feel like we’d always be able to tell it’s Phasma.
And although I was happy to trim her to remove the fight scene with Finn, I like Christie and I’d rather not remove more of her performance than I have to.
Still, I’d love to see it tried and would be curious to see how effectively it could be done!