Why? 2 Petals not open on Phal

[Helen]

Hi everyone,

My phal has 4 - 5 buds and the first has opened, but not fully. It has been 3 days and only the sepals have opened up wide and normal. The 2 petals are cupped loosely. I tried to open them gently, they moved out a bit temporarily and then cupped back up again. Has anyone else experienced this weird event? perhaps the window area is too cool? approx. 65 nite - 69 degrees daytime. Except, my other phal is blooming normally in the same location!
Thx
Helen