Phaleonopsis with many Blooms, Leaves Suddenly Yellow!

[rowdymagic]

Forgive my ignorance, I am new to orchids. I believe the one I have is a phaleonopsis.

I repotted one I was given about 6 months ago in orchid mix and it blossomed out beautifully, has about 40 blooms (photo attached). I water it thoroughly once a week, and it has holes for drainage in the bottom of the pot.

However, in the past week or two, suddenly the leaves are turning yellow, and one leaf has a whitish patch on it (second photo attached). Is this some kind of insect? Disease? Too much sun? Normal die-off? There is also a new leaf coming in in the middle - is this just replacing the others, which are naturally dying off?

I live in Southern CA and it has been pretty warm until the past couple of weeks - about the time the orchid's leaves began to turn yellow. The plant gets full sun through a window for about half the day, but it is cooler now. What would you suggest?