I don’t think light is the problem. That leaf looks like it has a cracked on the seam. Maybe that lead to an infection? Sun burn happens on surfaces 90 degrees to the sun. That leaf look turned down so it would be out of direct sun.

I would cut it off about an inch into the green part then dust with cinnamon. Remove the lower dead leaf as well.

It also looks dehydrated, so if you can put it in a bucket and fill it almost to the rim of the pot and let it soak for an hour or so. Then water more often after.

How long have you had it?

Hi James - Thanks for your response! All the leaves have it except the new one which seems healthy. It's weird how the purple is only on the tips. Here's another picture so you can see the other leaves and the whole plant better. As the it gets warmer they do need more watering and also are getting more direct light in my garden window which faces northwest. I've had it about two years. It bloomed great this year. I'm soaking it now.

That is odd. In the photo the discoloration looks black, but you said it's purple?

The marks looks uniform so I'm thinking so kind of environmental damage now.

When it was in the window, were the areas that are now purple touching the glass?

When you look at the whole plant you can draw a circle around the affected area, like the center was protected somehow. My guess now is that those areas were too hot or too cold because of it position in the window.

If the tissue is firm and not spreading leave it alone.

Some healthy Phals show that purple tinge, others never, probably depends a bit on ancestry, but the few in my collection with the tinge do not have that purple colour arrangement. (more spread out and diffuse)

I agree with the comments made by James in that the plant looks dehydrated and perhaps it is getting too much light. Winter here and the direct sunlight coming through a window is filtered by a matchstick blind.

Recommended temp range not below 60F not above 90F.