Hi tan, those aerial roots definitely should be misted / fertilized. If it shriveled, you more than likely didn't provide it with enough water. Any aerial roots should be watered and fertilized at the same time you water and fertilize the pot. And, since aerial roots dry off quicker than roots in a medium, you can even mist them every morning to good advantage, especially now, when summer's coming. Phals will put roots out all along the length of their "stems," many times right alongside or on the other side of a flower spike. If you don't water those roots, the plant won't get the moisture it needs.