Repotting Phals- Trimming roots and pot size

[flyfishdoc]

This is my first post. I have learned a lot from the board. A few random thoughts tie in here. I purchased some orchids from a grower who pots in sphagnum. I guess for them they are easier to keep moist. I have kept them in the original pots for 10 weeks now, and they are in ceramic pots to keep them from falling over. One has flowers that are just now dying, so I just repotted this morning, having learned from the threads that I can safely do this. The moss is mushy after 2 weeks of not watering. the plant is in the south window, tolerating half sun for the past month (when it got too cold to leave out). Half the roots were yellow and soft. I trimmed them off and kept everything that was green and firm. I did not trim the size of the long beautiful roots. My other phals are in all bark and in ceramic orchid pots (the ones with the holes) without plastic, and are doing very well for me. So I repotted from moss to a mixture of 50% bark, 25% perlite, 25% charcoal and a little moss.
Questions: 1. Are the ceramic pots not allowing the plastic pots to aerate, therefore allowing the moss to be too wet too long?
2. Can you cut back too much root? My gut feeling after readings here is that you trim what needs to be trimmed. Do you trim back the size of the long healthy roots when repotting?
3. What is the expected size increase for a phal for the next 2 years? I can see from my cattleyas how they are growing. But phals don't grow the same obviously, so how do you know what the correct next size is? (I did repot in the same pots-there was no need to go larger)