On Saturday 2/2 I picked up a Phrag. besseae 'Colossal' that was in bud. It bloomed later that week and held its first bloom until today. This first bloom lasted about 18 days.
Two more buds are ready to go (see pics).
Does this variety hold only one bloom at a time (and for only 18 days?), or do I have some other issue?
Most phrags have the tendency to drop seemingly-healthy blossoms as they open, or about to open another.
Frustrating as hell.
As to the life of each blossom, it's hard to say, as your conditions and the general health of the plant can affect that, but 18 days seems reasonable.
Yes, they seem to hold only one bloom per stem and as the "seemingly healthy" bloom drops off, the bud below it opens. As your plant grows you'll get more stems and they will also branch so you can end up with lots of flowers!
My single spike is on its third bloom, with two more buds in development. I certainly can't complain about the number of blooms, but it has consistently dropped the old blossom the day before the new bud opens.
Consider the Paph, then. The one blossom opens (finally) then lasts for months then one day just drops. No replacement until the next fan is ready. I think you are lucky with multiple flowers from same infloresence.