Would I be foolish to sprinkle a small amount of worm castings over the potting mix in my phalaenopsis orchid's pot?
Worm castings?
Yes. And if I'm guessing correctly, you should switch out your "potting mix" for orchid bark, available at any garden place, or even in your local supermarket floral area. Phals need to have good air circulation around their roots. Regular potting mix will be too heavy. It's odd that many of them come in regular potting mix, as it's not the medium of choice for them.
Get a terra cotta pot (not necessarily an "orchid" one, with the holes) fill it 3/4 to 7/8 full with the bark, and nestle your Phal's roots in as comfortably as you can. Then top off with more bark. Keep the crown above the bark line. That should be ok for a year or so. Check the bottom occassionally to see if it looks like the bark is breaking down. When it's mushy, it's time to repot. I don't bother with humidity trays, I take the whole pot and soak it in a bowl in a light fertilizer solution weekly. A good sign of Phal health is when you get the greenish windy roots traveling over the bark.
Hope that helps-