Seemingly stagnate Phal question

[labyrinth1959]

I have several Phals all are doing very well except for one which seems to have gone stagnate with respect to new leaf growth. It presently has a very nice yellow flowering, but it has not put out a new leaf in over a year. It has recently sluffed off a leaf(very gradually went brown and dried up over a period of several months) and now another leaf has just begun to show a bit of browning on the very tip of another leaf. Currently this plant has only four leaves while the others have 9 -15. This plant gets the very same treatment as all the others which are growing and flowering very nicely. I am befuddled as to what might be the issue with this particular one.