Congrats on getting your orchid to rebloom! When it has finished blooming you can cut the spike off - I usually wait til it browns and dies. Some Phals may grow keikis, or branch from a node on the spike.
Different people use different media for potting Phals - probably the easiest to obtain would be medium fir bark mix for orchids. Bark mix should be soaked for a few hours or more before using (tho I have repotted using unsoaked dry bark, and soak the pot after repotting). Only go up a pot size if the roots will not fit back into the same size pot. Make sure the pot has good drainage.
If your Phal is currently potted in sphag moss, bark will need more frequent watering - new bark mix will also dry out faster than older for a couple of months, so adjust your watering. If it is currently in sphag moss, and that has worked well for you, then you could definitely repot using that - but for many people it retains too much moisture and is difficult to not over-water.
GL