Only 2% of the population can effectively multitask.
When a recruiter calls, the first impulse is to take that phone call no matter what.
Timely replies are important. But if you are really pressed at the moment, it’s okay to reschedule the call for a bit later in the day or offer to call back in 10-15 minutes when your hands are to that full (literary or figuratively).
Remember: our brain isn’t physiologically wired for effective multitasking.
On the contrary, when you are forcing your brain to switch back and forth between different things, it goes into distress and fails to properly focus on either of them.
As a result, when you multitask, you are very likely to miss important information or make stupid mistakes.
So don’t do that during job interviews : )