If repotting is what you really want to do, then I think you should. Phals don't seem to mind it and they often continue to bloom after being repotted. When I repot a phal in bloom, I don't do any root trimming. I just try to remove most of the old material and gently repot it in new medium. Don't overpot, keep it in the smallest pot that the roots will comfortably fit in. Good luck.