I have a Phal. that is only a few years old, and it is growing tall, like a corn stalk, but much, much shorter. I wonder what the future holds in store. Will the plant get really long, like a vine? Will it be more likely to keiki and form a clump?
I do remember seeing about 12 years ago a Phal that the main stem was about 2 feet high. It had produced a keiki that was never removed and was about a foot tall.
Depends on the plant and growing conditions. I have seen photos of Phals in Asia that were just huge. My oldest one was purchased in 1989 and is not any taller than my other plant. Blooms like clockwork every year, though.
I don't have an old one, but I believe the size can depend on the chid and the culture.
Some of them keep loosing lower leaves and so each time you repot you move it lower in the pot and eventually cut the bottom off the stem (the roots also tend to start growing from higher and higer up the plant).
On the other had I've seen pics of some massive Phals and one or two of mine don't seem to be loosing their lower leaves and given time and a continuation of the way they are going could get massive.
You mention yours is growing tall. I understand it is a trait of Doritas to grow taller and if a Phal has a lot of that in it's parentage it can have a tendency to have a greater gap between the leaves.