I can also confirm the link between water hardness and leaf gloss, but can’t offer anything except further speculation about the reason. When I get phals from locally-grown sources, the new leaves they grow once under my care are much glossier. I use RO for most waterings, and by the visible layers of water spots on the plants when I receive them, it’s clear that the greenhouses use tap/well.
More than the dullness of the leaves, there appeared do be some wrinkling. That is what made me think "underwatering". That, and the coarse medium. I have watered plenty of Phals with "liquid rocks" out of the tap and still had stiff, glossy leaves.,