Hello everyone. This is my first time to post! I grow orchids in an inherited greenhouse in North Texas. I have some experience but am not an "expert grower"

These phals were perfectly healthy when repotted in June in a fir bark mix. I am extremely careful with watering. I started noticing a problem with the leaves looking mottled maybe a month and a half ago. At first I thought it was a nutrient deficiency but it progressed. Now I see spots on some leaves and discoloration on others. I threw some away and when I dumped their mix saw that the roots that were planted were totally dead but the air roots looked healthy and thriving. I don't want to lose all my plants! Please help! I sprayed with Phyton 27 on Monday.