Is this Phal just losing old leaves or is it a problem?

[AEKass]

One of my phals developed 3 yellow leaves in the past week. I'm not sure if it is just shedding old leaves or if there is a problem. I repotted the orchid a few weeks ago after it dropped its flowers (I also cut the stem when it started to brown). I have photos of the yellow leaves and a photo of the roots in the new medium I repotted it in.

As a bit of background, I moved from northern California to Boston over the summer. My orchids are now near a northwest facing window. I water about once a week (depending on how they look) and use sink water.

Are they yellow leaves just dying old ones? Or do I have a bigger problem?