Departmental rigor/reputation is more important/narrow in philosophy than in may STEM subjects. In the US, that means that a top philosophy PhD program will be chock full of Ivy/equivalent/near-Ivy grads with almost no representation from “regular” schools besides Rutgers and Pitt (which are 2 of the top unis in philosophy).
Looking at this
http://www.philosophicalgourmet.com/overall.asp,
It seems like Oxford is best by far, Cambridge and St. A’s are good, and you shouldn’t go below Edinburgh/LSE/KCL/UCL.