How does one assess one's chances of getting accepted into a PhD program in philosophy?
As everybody in the comments are saying, this is a very individualized thing. However, to get a good grasp of your standing relative to other students, I would check out thegradcafe.com.

Yeah, thegradcafe is an especially anxious and paranoid subset of grad school applicants, but you can see what kinds of applicants got accepted or rejected by checking the app board or skimming the forums. There's a dedicated Philosophy forum.