How do I fix my dying orchid?

I've looked all over online for an answer but it just got me more confused on what to do. I repotted my phal orchid about 3 months ago and now it has lost two of it's bottom leaves and is yello at the base. I used Miracle Gro Orchid Mix to repot with and the pot I used was twice the size of the last one. It lives in my basement with little light and a nice cool temperature. I noticed that the soil was drying out much so I waited to water it. Now it's dying. What did I do wrong. Over water, underwater, not good enough drainage, wrong temperature... I haven't a clue. I'm new at this.