Is this rot on my phal?

[Kayt]

I purchased this phal from a general garden store a few days ago. From what VERY little I know it looked fine. Yesterday I noticed a thin layer of mold growing on top of the sphag moss so I re-potted it and another one of my older phals today. This is the first time I've ever re-potted an orchid and I noticed a big difference between the two. The phal that I've had for a few months now had lots of green and white roots, while the new phal has less roots and many of them were brownish and spotted. The one big thing that I'm worried about is at the base of my phal, where the leaves meet the roots, it is dark black. Does this look like it's rotten or is this normal? Will this guy be okay?



This phal was planted completely in layers of sphag moss, while my older, healthier looking phal was potted in a bark-type mix.