I believe that for now you just care for the mother plant as you normally would. As for when to remove the keiki you should follow the 3" root rule, wait until you have either 1 root that is 3" or 3 roots that are 1" or any variation in between. I've read of fertilizers out there that encourage keiki root growth however I have never used any so I'm not sure if they are worth the extra cost.
Right now I have a phal that has been working on a basal keiki for over 4 months now, it is still so small although it is easily twice as big as it was when I first discovered it. Everyone on here isn't kidding when they say that phals are slow growers.