Phal: Great roots, bad leaves. To fertilize or not to fertilize?

[Bud]

You need to feed your orchids. That is why you got to give them fertilizer.
If the roots are good then you need not worry. The plant will produce new leaves provided you give it proper culture.
There is nothing you can do about the cut leaves. Although the burned leaves can develop fungi infestation if there is yellowing around the burnt areas, then you need to cut it off to save the healthy part of the leaves.
The way I look at your pictures, the plants are going to survive with its surviving leaves left and grow into a magnificent plant once again.