You can even repot a Phal while it is blooming... the ideal time to pot any orchid is when it is starting to grow new roots. Some orchids (such as Catts) make new roots only once or twice a year, and sulk if repotted when they're not actively rooting. Phals are growing roots all the time, so any old time is fine. Getting them into fresh medium that gives lot of air around the roots is really important. (Phal root want "humid air" rather than "wet".