Phal w/ Dying Yellow Top Leaves EMERGENCY! !

[missjones12383]

Hi,
First time poster. I've had my phal since this late summer and have it sitting on a table near the window with medium to low light. I repot it in Aug. I noticed about 2 months ago the leaves on the top turned yellow. I used hydrogen peroxide to clean the roots thinking there was a problem there. I also had to clip the roots and repot again in October. Nothing is wrong with the bottom leaves. The medium I use is better gro special orchid mix. I haven't used fertilizers since I got it and water once per week. I took pics of the temp of the sun room it's in. I'm just not sure what to do. The roots were not rotted when I used the peroxide a I just figured it was the medium. Some were dry and yellowed. Help!

Thanks,
Beginner