You and I are in similar zones. Mine just recently started to spike.
3 out of 7 is a fairly high kill rate.
Typically Phals don't just die overnight. Some plants will go downhill quite rapidly. Usually the death of a Phal is fairly prolonged.
How many years have you had problems? Several?
Something environmental has to be the problem unless it is watering related. Indoors, Phals usually do pretty well - too much direct sun can be a problem.
