It just depends on the root-mass, Victoria. You don't really need a pot larger than what those roots will comfortably fit into, but any roots that are growing above the potting media, let them stay above the new orchid media. I like to use clay pots with all my standard size Phal, simply because they can get top-heavy and the clay prevents their tipping over . Also, be sure you angle that plant so that water will tend to run out of those top leaves (the crown) rather than remain in those leaves. That helps prevent crown-rot. Also, be sure you have plenty of drainage holes. Phal. love moisture but don't like "wet-feet". You don't want your media to retain water.
