Well, here's a nickel's worth:
Aerial roots are not an indication of problems with the medium, but are a sign that the plants are putting on enough vegetative mass (leaves) that it feels the need for more mechanical stability (which it would get by attaching to a tree in nature, but cannot in a small pot).
That is not to say that there isn't an issue with the medium - if you're judging moisture by the top of the moss as you state, then you really have no idea what is going on down in the pot where it counts, and that's the important information. Pull the plants out of the pot and check. If the moss is soppy or so compact that the roots cannot "breathe" freely, repot. If the top only dries out every 10 days, I'd bet you have issues in the pot.
Your bark/charcoal/perlite mix is a good, all-around staple, but you might want to add about 25% sphagnum to retain a bit more moisture for the phals. Before you use it, pour lots of boiling water over it, as that "opens up" the bark to absorb better. Repeat with lukewarm water about 15 minutes later, and it'll be ready to use.
With a 20-10-20 fertilizer, I'd recommend 1/2 teaspoon per gallon for feeding every two weeks. Withholding it from the dendrobium might be OK, too, but not the phals if they are actively growing.
Dr. Yin-Tung Wang, then of Texas A&M, did a study in which he showed that phals need about 10 days to two weeks of an average growing temperature decrease of 10°-15° in order to initiate spikes.