I have a phal that up until last week looked as healthy as can be. New spike, old spike with new side shoot, leaves green and trugid - very nice. This past Wednesday the lowest leaf started to turn yellow all over and today it is bright yellow - still turgid but very yellow.

Climate where the orchid is growing has not changed since I got it several months ago. It is watered every Saturday morning. No bugs that I can see. No crown rot that I can detect. It never has wet feet.

Any ideas what is going on with this orchid and what if anything should be done with it?

Thanks...