I love phals...lovely flowers that last a long time. Look around it's area and make sure no airvents are around. Hot or cold drafts blowing on the buds will cause them to blast. Also; you might want to add a little bloom booster fertilizer into their weekly watering. Every fourth week, just use plain water to rinse extra fertilizer salts from the pot. If the problems continue, you may want to check the quality of the water you are using. Usually though, with phals, there is a hot or cold draft causing your grief. Occassionally it is the humidity, but it sounds like you have already thought of that.
Good Luck! I hope we get to see some pictures of your flowers soon.