It could be some as easy as not getting enough water when in bloom.
You're phal is in sphag moss? Its might be time for a repotting - with moss it should be done before 1 year (IMHO)
Phals can take some direct sunlight - depending on the time of day. I have some of mine facing south but I'm in Canada, and this time of year the sunlight really isn't that strong yet. I check the leaves for heat - if they are warm I leave be, If they are hot, they're moved or the curtain gets closed off.
A sheer curtain would provide some kinda filter from the harmful rays.
Knowing the conditions of the roots and A photo would be most helpful