Looks like sunburn.

It's 6-7 inches from 2 T5 fluorescent bulbs. My uncalibrated cell phone light meter app shows 300-350 fc.

An identical Phal that has smaller degree of discoloration like this is on another shelf 9-10 inches from 2 T5s, and the light intensity measures there at 800-850 fc (I guess that reflector is better and/or lamp position is more directly above).

Does not look like the light is too strong from these numbers. I touched the leaves, and they do not feel warm, so it's not the lamps' heat either. What then?

I agree it looks like some sort of heat/cold damage. It could be bugs but I can't tell from the photo. If the new leaf looks healthy, I wouldn't be concerned. What bothers me is the size of the leaf. It should be larger.

I would fertilize and water the plant to get full growth on the newest leaf. If that leaf stays small it suggests the plant isn't getting enough light.

Jane

The youngest couple of leaves are small likely because it was missing almost all the roots when I got it 11 months ago. I am hoping for larger leaves, 'cause roots have grown a lot since then.