When the keikei on your dendrobium gets roots about 3-4 inches long, and has at least 3-4 roots you can detach it from the p-bulb with a sharp blade and repot it in a mix suitable for a baby plant.
As for your phal with the roots stuck to the pot. If it is a clay pot, it is best to break the pot apart and leave the pieces attached when you repot. Try to get the pieces small enough to fit in your new pot. If it's a plastic pot, a few squeezes here and there and a pinch at the bottom of the pot will let them loose. One nice thing about plastic is that the roots do not permanently attach. Get the roots wet before trying to remove them from the container and they will be less prone to breaking.
Also; I have found that if I find a plant to be rather healthy in it's original container and mix, I try to replicate it as closely as possible. It is less stress on the plant.
Good Luck, hope this helps