[jerrymeola]

Lack of moisture, cool weather, lack of light, old age any or all of them.

Why do we cut our hair or nails. They are no longer needed.

If the new growth is green and firm then the plant is growing naturally.

I have mentioned before that Phals grow down from tree branches so when we pot them upside-down it is not natural. In nature the top of the leaf (now the bottom in a pot is not light sensitive, while the bottom (now the top) is super sensitive normally only getting bounced light from the ground.

In nature the leaves spiral exposing half of each leaf. In a pot they overlap. If the lower leaf does not get light in the pot, it will die off as unnecessary to the survival of the plant.