kewpie, dilluted at 1/4 strength, you should be fertilizing with every watering, and flushing the medium each time. The way you're doing it, spraying to moisten the tops, doesn't let you leach away any excess fertilizer or mineral salts. If that will keep things too wet the way your compots are set up now, you might have to re-compot, using a layer of sphag at the top that's only an inch or so thick, above a base of styro-peanuts or something else inert that provides good drainage. (That's the way I do it here when I compot in sphag.)

Assuming that your other conditions are appropriate, I would say that the yellowing you're seeing in the Phals is definitely a nutrient deficiency. Phals need a good amount of calcium and magnesium, so if your fertilizer isn't providing that, you'll have to supplement. You can add calcium either in liquid form or as a top dressing by putting down a layer of crushed oyster shell or diatomite, and the easiest way to add magnesium is to dissolve 1 tablespoon of epsom salts in a gallon of water before you add in your other stuff. (Or, instead of all that, just use Peter's Cal-Mag fertilizer on your orchid plants.....)