Rapid yellowing of Phal leaves

[Tukatuka]

Hi everyone,

We are in Indonesia and we have a Phalaenopsis that we have had for over a year. It is tied to a tree and after many months it has finally attached at least 3 healthy juicy fat roots on the tree trunk and had around 7 leaves. No blooms, but I suspect that's due to lack of sun.

Problem is within the last week, the bottom leaf turned yellow over 2 days and dropped off. I know Phals do this, but unlike my other Phals whose leaves turn yellow and dry before it fall off, this one is still juicy. And to make matters more worrying, the second bottom leaf started to turn yelloq very quickly too. Another leaf started to turn yellow at the edges and I snipped the yellow part of before it can spread. The body feels fine and the plant overall looks alright to me.

Is this still considered normal?

Thank you