Pleated Leaf on New Novelty Phalaenopsis

[Ray]

There are no “hard and fast rules” about such things, as a multitude of things can lead to the same symptom.

In my opinion, the yellowing and dropping of a lower leaf is sometimes due to underfeeding, as the plant is forced into drawing nutrients from it to send them to newly-growing tissue.

“Pleated” leaves is a common occurrence in oncidium, not phalaenopsis, and can be due to insufficient humidity or insufficient water uptake, but that can be due to underwatering OR a compromised root system.