Sarahke where are you located?
I have all my orchids in a window facing ESE. It seems to be enough light for mine, as they are all seemingly happy. However, I have a Phal gigantea in a window facing WNW, so it's similar direction to yours...and it seems to be doing well. It's growing. So the NW window may be enough light for your Phals..but the best way to find that out is to get a light meter.
