I have not been able to be in the woods much yet this year but all of the squirrels I see around us in the southwest corner of Michigan are all black phase squirrels. I have not seen a regular fox squirrel all year.
The black phase squirrels seem to have come farther and farther south over the years....I don't think we had any 3 or 4 years ago. We seem to have more and more and now they are the only ones I seem to see.
It sounds like grey and fox squirrels can both go through a black phase and we mostly have fox squirrels but these black squirrels all seem smaller than the fox squirrels we usually have. There doesn't seem to be a shortage of them around here, though.