If a leaf is developing high up the spike, you may be getting a keiki.

It most likely IS a keiki and you should let it grow. Be sure to water/fertilize the roots it produces and when they get to be about 3 or 4 inches and it has at least 2 leaves you can cut the spike and pot it up. I have 2 Phals that do this frequently & sometimes I just attach a 2" pot to the 6.5" pot and leave the keiki attached to the spike while being potted in the 2". When the spike dries up I cut it off (like an umbilical cord !) and then have a separate plant !

I have a favorite harlequin phal that produced a keiki on a spike and I've had it pinned in a 3 inch pot for at least a year. Now 7 inches across,double leaves and still no roots. In the meantime the mother plant does not produce. I'm sticking with it though. Love the white burgundy velvety flowers and want a second plant.