This has happened to me twice. I am more than willing to give you a quick phone interview, but I AM AT MY JOB DURING THE DAY. I can take 5-10 minutes out of the workday if it's scheduled, but if you call me without any fore-warning I am usually in the middle of doing something.
The first time this happened, I chuckled when asked what time they could call back because I was in the middle of doing a big project – to which the recruiter took as an insult and basically just hung up on me. Is your skin that thin that you can't deal with a little chuckle?
The second time I asked for them to phone back in an hour – that was an hour and a half ago. Now I'm sitting here on reddit with the time I carved out posting this post.
Seriously recruiters, step up your game. I get that you guys are having a hard time finding people, but an iota of professionalism would be nice.
/Rant