Welcome to the forum.
The first thing is that you need to understand that epiphytic orchids, like your phalaenopsis plants, do the majority of their gas exchange processes through their roots, so it's essential that there be lots of air flow to them. The plastic pots and densely-packed sphagnum, when watered, are likely suffocating them. If you simply moved them into bigger pots and loosened-up the moss, it would be an improvement, but frankly, the moss looks pretty old, so I would repot into fresh material.
The black stuff is likely mold, probably associated with the aging moss. The purple coloration is normal in some plants, and may be indicative of the flower color, to some degree.