Bottom Leaf on Phal Turning Yellow on the Side

[Torja]

Hi,

I'm a beginner in caring for phal orchids. I've managed to kill two of them. I recently bought another phal and want to make sure that I take care of it properly.

I've noticed that the bottom leaf is starting to turn yellow on the edge, and has begun to spread towards the middle of the leaf. All the other leaves look healthy and strong, and my plant continues to bloom their flowers, with new buds opening up each couple of days.

Does anyone know what is wrong with it? I keep it in a pot with moss that has a drainage hole, and it sits on a table in front of a window with northern exposure.

Any feedback or advice is appreciated, I'd love to make sure that I can keep this one! Thanks.