when to increase a phal pot size

[ladyslipper]

This is really a basic question & I admit I am a little embarassed asking it but other than to replenish the medium, how do you know when to increase the pot size of a phal? I have had phals almose climbing out of the pot and the grower told me just to renew the medium as the pot size was fine. The plant in question was the phal amabilis but I have found this same question occuring with different plants. Do you just increase the pot size until they are about a year or two old?

totally confused

mary