Phal bellina bloom duration?

[bottlemarkercup]

When I bought my phal bellina it had one open bloom (and several buds). After a couple days the first bloom withered and fell off, but subsequently another two blooms opened. Now it is preparing to open a third bloom. However, it seems like one of the open blooms is about to wither as well. It has been open for approximately three weeks.

How long should I expect phal bellina flowers to last? I thought it would be a bit longer than three weeks. Is that too short?

Also, should I be caring for my blooming phal any differently than regular? More fertilizer? More frequent watering (currently every 3-4 days when the medium is dry).

Thanks!