When you call a musician on the phone there is about a 30% chance that they are practicing and will find the interruption to be very annoying. Hence the brusque way of answering the phone. I have been known to shout out a string of curses upon hearing the phone ring. I then suppress this and try and answer in a pleasant manner. I read a study done by a British university a while ago that stated that if you are working in an interrupt-driven environment it is actually worse than being under the influence of marijuana--that is, you lose about ten points off your IQ.
Classical musicians are one of those groups whose work can only be done in a certain environment: one that is utterly silent and free of interruption. You have to be able to concentrate for fairly long spans of time, typically thirty to fifty minutes. You also need to take occasional breaks. For this reason, in order to work at your maximum potential, you need the whole day to practice for perhaps five hours. Scholars and scientists have similar requirements. I recall Jordan Peterson mentioning in a video that he could only read for two or two and a half hours at a time. Of course he is not reading a newspaper or magazine: he is probably reading Nietzsche or Jung.
Doing any of this kind of work: tight focus on the sound, phrasing and articulation of the piece you are practicing, or close attention to not only what the writer is saying, but what might be implied, all this demands total concentration. At first you might not be able to keep it up for more than ten minutes at a time. If your attention is wandering, it is best to stop and take a break. But over time you can increase it to twenty minutes, thirty minutes, perhaps even an hour. After all, there are classical compositions that are twenty or thirty minutes long for guitar and even an hour long for piano.
So the next time you phone a musician and he seems to answer a bit curtly, just bear in mind that he might have been playing Bach...