Phal leaf disease problem. Arthur

[lgorda]

Hello from Edmonton, Alberta (new to the site)
I have been growing orchids for about 8 years and have a small collection. Recently my Phals are showing yellow blotches on the leaves which are increasing in size and ultimately are turning brown. On some plants they cover about 50% of the leaves. Flowering is still normal. Have I got a virus? Temperature has been about 75 F but air flow was almost none existant.
Any suggestions are appreciated.