Phal. Leuddemania won't flower
 

About two years ago I bought an N.B.S. Phal. Leuddemania “Arlington”
from Parkside, it arrived in good shape and has grown well. Last year
it threw a flower stalk which is still there and very much alive but did
not produce any flowers. This year it threw two more flower stalks that
are both doing well. All three stalks show what look like tiny buds but
do nothing more. The plant is growing on a windowsill with natural
light. Five other phals next to it are growing well and flowering in
season. Any ideas on getting it to bloom? Thanks in advance