Which Orchid Mix do you use to repot your orchid in?

[Skayc1]

I'm a beginner orchid grower & have a phal orchid I've had for 1 year, it came in bark, It's roots are coming out the bottom of the pot. I'm wanting to repot it & repot some clearance rack orchids(also phals) I recently bought (I removed them from the sphagnum moss they were packed in & have the roots in the air for now after trimming off the damaged rotted roots) since the orchid I first got has done well in bark, I want to use that. How often to repot orchids in bark every year or every year and half? Also I know nothing about mixing my own mixes so are there any good orchid mixes sold in the stores?