Personally, I recommend feeding at every watering - OK, maybe 3 out of 4 if growing in traditional media - and at a dilute rate. If that's the Grow More 20-20-20, use 1/2 teaspoon per gallon.
As to drying out or not, there are two things to consider:
- What does that type of plant see in nature? For example, if you're talking phals, they stay wet all of the time, low in the tropical forests. Tolumnias, on the other hand, grow on thin branches of trees and shrubs in the Caribbean, where they will see lots of breeze and will dry out rapidly.
- How open and airy is your potting medium? As long as there is lots of good air flow to the root system throughout it, drying may not be necessary at all.
Remember, water does not cause root rot, suffocation does.