Phal roots dying after repot.. please help!

[Aslan14]

I have a couple of Phal's that I recently repotted and both are now suffering. One had just flower spiked when I noticed the bottom couple of leaves started to wrinkle then fall off. It ended up aborting the flower spike. When I pulled it out of the medium (mixture of fir bark and a bit of orchid "soil"), some of the roots were brown with white spots on them and obviously rotten.

The second one I potted in straight fir bark a while back, but just recently noticed the leaves not doing well. When I pulled that one out of the medium, all of the roots that were in the medium were brown and dead or alive with dead ends.

The first phal I mentioned I ended up repotting in a mixture of lava rock, charcoal, perlite, and small/medium fir bark. It seems to be doing better, the leaves have not continued to turn yellow and fall off.

The other one is sitting in a bowl right now and I soak it every couple of days, then just let it sit out. I am honestly afraid to repot it, as I don't want to lose the few remaining roots.

Was I overwatering? The second one was in a pot with good ventilation, it was an "orchid pot" with large holes in the sides. The first one was in a closed pot, but with good drainage.

I have heard that orchids are more forgiving if you underwater them than if you over water them, but for some reason it seems like I can't figure it out. I have 20 other orchids that seems like they are doing ok, a few of them are flower spiking (like my Zygopetalum, I cannot tell you how excited I am over this!!). But after this I am wondering if I need to rethink my entire process here. Some of my orchids rebloom so easily, and some are more stubborn, like a really picky oncidium that I have not been able to get to rebloom in three years even with good watering and fertilizer.

Any feedback would be great, thanks!!