I agree with all that has been said about plants going 'tubular' due to
culture problems. But from what I've seen Phals can go "tubular" for a
variety of other reasons.

Based on what I have seen, going tubular in some cases is just a natural
part of the plant's growth cycle and should be expected. I find many
Doritis and Kingidium species have this sort of growth habit where they will
only bloom off a plant a few times in the normal fashion before going
tubular and then sending out multiple new growths. These new growths
develop to blooming size quickly (as little as a year) and the whole cycle
is repeated. With these plants, it just does not take many years before
they have established themselves into a large clump or you have a bench full
of divisions. I do not find this growth habit very common with Phals as
described by Sweet, but I have seen a similar but slower growth cycle with
some aphrodite, venosa, and equestis plants. I posted a picture on ABPO of
a Drlla Nina (Drlla = Doritis X Kingidium) which has this type of growth
habit and has been allowed to grow without being divided.

I also see a fair number of tubular Phals which have come out of cloning or
stem propping. Typically these plant's first blooming come out as tubular.
In some cases this going tubular is just one of the problems that is showing
up as a result of bad cloning work. But in other cases, these plants put up
a new growth while in tubular bloom that when grown out always blooms
normal. On ABPO I posted a picture of a Phal Cassandra stem prop. It's
first blooming was tubular. But as can be seen in the picture the new
growth is sending out a normal bloom spike.

A couple of years back I had a large batch of a single clone that I was
growing in two different greenhouses. When the plants came into bloom, the
plants in one greenhouse basically all bloomed normal while maybe a third of
the plants in the other greenhouse bloomed tubular. The only difference in
the treatment of the plants that I can remember is the plants in the
greenhouse that bloomed tubular got some extra fungicide treatments. I do
not know if this was the cause or not.

Pat