Need Phal care help...Bad roots..

[Ornella]

Sheridan and others who can help... I am pretty sure my Phal has good roots inside the pot, because it is doing well - healthy leaves/new aerial root. I am just worried about dead roots above the moss.. Recently I moved Phal to brighter place and hope to get a flower spike... I do not want to take moss/roots out of the pot and disturb them before I have decided on a planting media. Does it matter when to re-pot it? Fall or Spring?
Also I did have one Phal planted in a bark ( I got it in Safeway) and it did not survived....I am still not sure what should I use as a planting media considering my DRY-DRY climate....I would really appreciate everyones advice!
Ornella