sticky substance on underside of Phal leaves

[ladyslipper]

Hi guys, I don't know if this is a problem or not but for the longest time, I would have 'chids who had some sticky residue on the underside of some of the leaves. These leaves are not totally covered in the residue but I am curious on what it is. It also reminds me of the crystals on sugar. I don't know if the plant is secreting something like maybe getting rid of excess salts or something. The plant looks great otherwise, it has even started to throw out new roots in preparation for new leaves and spike.

mary