This post might be entirely irrelevant, so I apologize in advance, but I've always had great success with phrags in primarily inert mixes, throughout the years. I've tried and experimented with lots of media, and more or less, my phrags have acclimated to and grown well in all of them.
My preference and my plants' preferences, as stated have always been for mostly inert mixes, with just a small percentage of organic components. The organic components, at least in theory, provide a small amount of nutrition as they break down, and most likely assist in pH and ion regulation.
My current mix, which I've stuck with for nearly a decade now, is rockwool based. I add large grade perlite (sponge rock) and aliflor/hydroton (or other LECA) as the base. Then I mix in some charcoal and spaghnum to round out the mix. Minor constituents include egg shell, bone meal, and oyster shell "to taste".
This applies primarily to water loving phrags, but honestly, I grow almost all my orchids in the same mix, and they all seem to love it. Even the caudatum type phrags enjoy it -- I simply water those less and avoid leaving them in sitting water.
I shy away from primarily organic mixes due to experience, though I have no experience with orchiata. Bark mixes break down quickly, and while phrags mostly seem fine with this, other orchids do not. Overall, I grow best when my collection is in a consistent mix. Coconut husk was okay, but while plants initially did well in it, over time, they failed to thrive. Maybe it was salt build up? But, rockwool supposedly has the same, and yet, it works really well for me.
I guess if you were to take any advice from me, it would be that most phrags are ambivalent to the potting mix as long as specific requirements are addressed (i.e. water lovers kept wet, others allowed to dry out a bit between watering especially in winter).