Yellow Leaf midway up an otherwise very healthy Phal

[RosieC]

Hi everyone,

I was shocked this morning to see a yellowed leaf half way up one of my Phals.

This Phal is my largest. It has 14 leaves, masses and masses of roots which hardly fit in the pot and currently has two massive flower spikes.

(See this link for a pic of some of it's flowers just now...
Picasa Web Albums - Rosie - Orchid Display)

But I'm really really worried about why this leaf has gone yellow. If it was the bottom leaf I would not be so worried. If it was the one I partially broke while repotting a few months ago I would not be so worried (that one is still nice and green). But I can see no reason for this colour change. I'm pretty sure the leaf was fine last weekend when I watered this 'chid (I check the plants over every time I water them).

Sorry about the pic quality, I snapped them quick as I rushed out to work this morning. The sunshine is morning light, but it's not even been in that position recently but closer to the center of the room (so not sun-burn.)





I really hope there is not something seriously wrong with my Phal but if there is I want to catch it quick. What should I be doing?