I was curious to see what would be an explanation but I have a theory based in my experience with a phal that was under too much light in summer. A new leaf curled as it was growing to minimize, I think, the area exposed to light.
I've out it further away from the window and have turned it to force to get a more natural position (it was curled and bent) and slowly if has uncurled and nos has a more natural look.
It doesn't seems to be harmful because it's growing a spike.
I believe it's just a defense mechanism...it happens also when plants are under too much heat. They curl probably to prevent excessive water loss by transpiration, also acting as a refreshing mechanism due to water accumulation in the confined space created by the curling.
Just a theory...
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