Sphagnum itself isn’t bad, it’s not the best choice of media for a beginner with a Phal, but it’s not evil. I have a lot of things in straight sphag, even phals, even in my super wet and humid climate. You just have to understand how it works in your environment and if it works for your orchid, that’s all. I think people run into problems with this stuff because sphagnum can hold a lot of moisture, it breaks down quickly, and also with temperatures (if the orchid is wet and cool in sphag that can cause major problems in the root zone for warm growing orchids since pot basically turns into a mini air conditioner due to evaporative cooling)
For example since we are talking about Phals:
I have a few no ID hybrids that I keep under my balcony out of the rain that are grown in pots, the rest of mine are mounted hanging in the courtyard. The ones under the balcony are in smallish (under 5”) clay pots. The clay is porous, it breaths, and provides air. For some of mine, I might take a few packing peanuts and put them in the center of the root ball. Then I
tightly pack sphagnum around that whole thing, trying not to break the roots. I don’t worry about getting any media in the center of the orchid, I like to leave that open little air pocket, I just start wrapping the moss all around the outside of the root ball so I end up with a wad. Then I just stuff that whole mess in the clay pot. If the sphagnum is too loose it holds too much water, doesn’t dry out, the lovely long moss fibers collapse, and will not allow air around my orchid roots. When it’s nice and tight, that works with the clay, gets evenly moist, never soggy, evenly dries, and stays just airy enough. I started growing some of my phals like this 3 years ago, it’s the happiest they have been and my root growth has been amazing. You just have to find what works for you, in your environment, and your style of growing. There’s a thousand ways to get the same results but phals with bark is a great place to start