Well, here's what corporate says, and according to the square footage table on the bottom, as of this past February, the Philadelphia City Center (sic) Macy's had 386,000 square feet. It is, however, likely that part of the discrepancy is due to the store offices which fill a third of the third floor...
Also remember that prior to becoming Macy's, this space was a Lord & Taylor, which usually only takes up 150k sf as compared to the at least 500k sf a downtown Macy's would need.