You are talking (I think) about semi Hydro culture. Put Semi Hydro in the search box at the top of this discussions page to find. Maybe something in those long past threads will help.
Most of the Phalaenopsis culture notes on the net relate to the conventional culture methods.

Neil, I tried and failed at the same thing in the same way. I honestly think the key is that you have to do the transfer to the Semi-hydro when new roots are just beginning. The way I understand it is that most of time the old roots will rot, and that is why you have to have new roots started and ready to grow into the new environment adapted to it. I didn't have new roots started in mine so they all rotted and suffered too. Bottom heat, like a seedling mat helps some, but new roots already starting is the key I think.

-Heather

Thanks, ginger9899, (Heather); do you think I should simply start over with new plants? I have read that the hydroponics (LECA pebble) medium allows more air to circulate around the root system, which is better for the plant. The packed bark/spagnum moss medium that the plants arrived in seem to spur root rot, so I'm trying to transplant all that I buy.

Agree with Heather - timing is important with any repotting of orchids, but especially when medium/culture is changing as drastically as from moss to semi-hydro.

Also, western sun in Georgia this time of year may be too harsh on the newly repotted orchids. Leaves may be yellowing because of this, in addition to because of the repotting.

Neil, by the way, I don't see any pics attached, I think you mentioned there were pics.

I am afraid I can't give any more advice regarding the semi-hydro as I am a failure at it and a beginner at orchids in general (only going on my second year of growing). I have had luck in bark, but not the semi-hydro. I have actually just put a paphiopedilum into semi-hydro this weekend to try, but it is growing new roots so I thought I would try doing it right and see if I succeed this time.

I kind of tend to agree with greentoe357 about the western direct sun though, be careful with that on phals!

Sorry I can't help more. Good luck Neil!

-Heather

I have found that phals do best in bark, or a bark and moss mix. If the roots are as bad as you say, and you want to try to save them, get them back in a bark/moss mix. Once the plants develop more roots, you can remove a certain amount of moss ... but with a damaged root system, you need to keep the humidity around the plant high in order for it to survive.

I pulled an orchid out of a coworker's trash, and though it lost all but two leaves and almost all of its roots, I finally got it to bounce back by wrapping the base loosely in moss, and setting that in a small, ventilated cup of bark. It was never soggy, but it was never dry. It grew three stunted, sad leaves over time, but it now has one large, beautiful, perfect leaf, and another on the way. When I saw that, I risked pulling it out of the moss to check, and there were six fat new roots growing through the moss.

YMMV, but I don't think a plant with damaged roots is going to bounce back in LECA.

I started experimenting with hydro over a year ago and it's worked great for my oncidiums and catts but not phals. They managed to bloom and grow aerial roots but the one or two roots that grew down started to rot. I've switched back to conventional watering until I have time to put them back in a bark mix.