This is how the very last bud on the spike flowered out! It has only 4 'petals' and no lip! Have you ever heard of such a thing?
Flower mutations happen every now and then.
A flower with that condition is called "peloric".
Some happen accidentally such as in your case. It appears that only one flower "messed up" but the rest are fine.
Some plants are permanently peloric due to genetics and continuously produce peloric flowers.
One of my phals does this on the last flower of each spike, each time it blooms. So I can tell the spike is done blooming when the flower like this with no lip opens.