The content doesn't, actually. I'll look up the specific case when I get home, but phone book publishers most definitely do not have any copyright claims to the phone number or addresses. They do have copyright claims to the font choice, layout, etc., so you can't copy the phone book wholesale, but you can take the phone numbers, rearrange them, and set them in a different typeface and you'd be in the clear.

I don't believe there's any part of copyright that takes the amount of effort into account. There was a case (again, I'll look it up when I get home) where a copy of a work that was in the public domain was granted its own copyright because it had a few errors in it. The errors were unintentional, but copyright was given. In the phone book case, the court specifically mentioned that even though there was no doubt a significant amount of work required to produce the phone book, that didn't give the publisher copyright.