How many old leaves is normal for a phal to drop at one time?

[Maru777]

Hello guys,

Need a bit of help please! I thougt that I was doing quite well with my phals. Had them since Feb. They’ve been growing nice new leaves and roots like they’re trying to take over the world. They looked pretty happy, but now 2 of them started dropping leaves. At first I was not worried because it’s the bottom ones so that should be normal but one is dropping the 3rd one already And the other one looks like it wants to drop 3 as well and all at once. The others I have only lost 1 each in the same time-span. Is this normal? Am I missing somehing? I added a picture for each of the 2 plants that worry me. They share a coffee table on my porch too so I’m worried if something got to one it will get the other.