I don't know how common it is, but I have a very similar-looking white Phal hybrid that I've had for about seven years now. The first couple years, it was fairly normal in that it would put out a new spike in the fall, bloom, and drop the flowers the next spring or summer before starting over again in the fall.
But the last several years it has been pretty much in perpetual bloom, with old spikes producing more buds on the ends, putting out secondary spikes from older spikes, and putting entirely new spikes out while old ones are still flowering. It's my most prolific bloomer!
As far as what you are doing right, I would have to say that is whatever you are doing. It really likes your combination of temps, light, watering frequency, etc. Very nice job!