Phal flower without all it's petals.
 

I think I might already know the answer to this, but thought I would see what you guys had to say based upon your experiences.

Last year, I was shocked when this particular phal did not fully open all of it's flowers. When I got it, it was not peloric. Now, it has many flowers blooming properly except for one.

This particular flower only has one of the outter petals, one of the inner petals and the inside of portion of the flower. It does not appear to have been eaten, broken or anything else. For all intents and purposes, it appears to have "grown" that way.

Why do you think that happened?

If I've understood correctly peloria is genetic. And so the plant you have may show different sorts of deformity or peloria when it bloom or then it can even look completely normal. Sometimes the way the flowers turn out can be influenced by changes in your growing environment and by stress that the plant experiences. And at other times even though the plant has not revived any stress or strain the genes kick in and it blooms in bizarre and beautiful ways. And then with no real reason or better growing conditions and the plant flowers normally!
Peloria is very interesting as you never really know what kind of flowers you'll end up with. Personally I enjoy peloric phals. :D
Do you have any pictures?

This could be genetic or environmetal especially if its a young plant or was stressed. Chances are the time it blooms all will be fine.
Joann