Phal leaves turning yellow and falling off

[kochsydn]

I think my phal is dying. The leaves are yellowing at their base and falling off. There is no spotting or other signs of damage. No sign of crown rot either. I also have taken the orchid out of the pot and the surface roots have all dried and withered while the deep roots look like the beginnings of root rot. 5 leaves have fallen off in the past 3-4 days and now only 3 remain. Is it salvageable?

It is because of over-watering or under-watering that the roots are in such bad shape?

I didn't sterilize my scissors when I cut the spikes after their bloom(3-4 months ago). Could it be infected?