Loss of the bottom leaf may be normal.
Changes in temperature can cause some leaf drop which tends to be rather sudden and involves more of the plant.
Phallys like it hot, humid, and breezy. They naturally occur in trees and on cliff faces in accumulated debris.

Here is a link that might be useful: Natural habitats

Does the pot it's in have adequate drainage? Phals love lots of air at their roots and don't particularly like wet feet which will rot the roots. Also, even though they are low light plants, they do like lots of bright light.