My first Phal was a large gift plant. Leaves were 9". Spike 30".
I then started buying small NoID Phals on sale in the grocery stores. Leaves 4". Spike 12".
There is no room for large plants in my home.
If the leaves are small when the plant blooms, is this an indication that the plant will stay small?
Chances are the plants that you buy blooming with a LS of 4" will stay on the small side and only get slighty bigger. They are bred to remain small, generally using equestris and other small species in the breeding.
I have one that I bought with a LS the size of yours and several years later it has no more than a 6" LS. but is alot taller.
Hope this helps answer your question.
I agree with Judi. Another attribute that I like about smaller phals is that the ones with short spikes often do not need to be staked. I like the natural look but huge spikes always need to be staked in order to display them.