Yellowing leaves and possibly yellowing roots.. What do I do?!

[Jaebird113]

Hello, I'm very new to orchid care. I just got a phalaenopsis orchid in February for Valentine's, and have been trying to do all the research I can to take good care of it.
Everything seemed to be okay, the flowers bloomed a while until early spring came and they drooped and proceeded to drop.
The leaves still looked healthy, and I was finally able to repot it since the blooms had dropped. I repotted it in some miracle gro orchid mix, and watered once a week or so.
I'm not sure if I have it the right spot for lighting.
Anyhow, just in the last few days did I notice that the bottom leaves on left and right are yellowing, and one came off completely. Another one in the middle has begun to yellow on one side.
I lifted the clear pot of of the decorative one to check it's roots, though im not sure what I'm looking for, and the roots are a mix of yellow and green.
Just want to know what it is I could be doing wrong, if there's anything I can do to save it from dying.
Thank you so much (: