If the roots are rotting again, it is getting too much water. Does the pot you put it in have good drainage? The water should run through the bark and the phals roots should dry off (not out) before watering again. Is you orchid sitting in a dish that holds water? Something is keeping the water in the pot. Unpot the phal and clean up the roots. Repot in a small, tight container that has good drainage. If you are potting him in a large container, the center (root ball) may not get enough air movement to dry off and that could be the problem.