We've made that connection several times in about the same timeframe (90 minutes) but it can be a nail biter. As previously mentioned, if your flight is delayed out of sxm or there is a long line at C & I, the heart rate goes up. Phily is huge and as WildBill said, terminal F is one heck of trek. There are bus shuttles that run within the perimeter of the airport (inside security) that can schlep you from the F terminal to either the C or A terminals. They have definitely saved some wear and tear on the old bods.

Here's a link to the shuttle info:

http://www.phl.org/passengerinfo/Pages/shuttle.aspx