Phal's are a mixed lot when it comes to heat. I have some that can do 90 and not wilt....others get above 85 and they "faint". The hotter it gets and the more you water, the more you need a fan blowing to keep air-movement going like really well. I keep my ceiling fan on medium and the front windows open for fresh air for the window sitters. My phals are always dried out by mid afternoon which keeps crown rot away. And don't overdo the a/c, it dries your air out and phals like 50% humidity. Alot of people try to compensate by keeping the roots wetter but that only causes rot.
Good Luck, hope this helps. There are other problems that will cause a plant to turn yellow and die...but the most popular is overwatering with insufficient air movement. I hope those with greenhouses chime in as well because rules for greenhouses usually differ from my windowsill approach.