black leaves on my orchid, help

[kimj]

hi,

I received this orchid 3 months ago, and a tip of one leaf had a couple of black spots. Now, the blackness has spread over all leaves but one. I thought the pot it came in was too small because the plant was nearly falling out, but I am afraid the current one might be too big. Is my orchid overpotted or is it infected? Any advice would be greatly appreciated, since this is my first orchid.
Thanks!!