I agree with others who have posted in this thread that the admissions committee probably can't or won't tell why you weren't admitted (although, again, it probably wouldn't hurt to ask). What I'd recommend is that you talk with your advisor or referees and ask them what they think the weakest part of your scholarly profile is and how you can start to improve on it this year.
This could be a strike against you, depending on how closely related your current discipline is to your interest in philosophy. If, for example, you're majoring in geology and propose to study German Romanticism you may have a hard time convincing the committee that you have an adequate background in the topic you studied. I should say that I managed to get into a philosophy program after majoring in Classics, but it happened to be a classics program that specialized in ancient philosophy and I proposed to work on ancient philosophy. In any case, if there is a possible gap it might be worthwhile to take a few philosophy courses, especially advanced courses in your general area of interest, or perhaps to take a few courses on other philosophical topics to give yourself a more rounded philosophical background.