One commenter posted a link to this Apple Support doc which offers instructions for when this same problems happens to an iPod, and some of the procedures can easily be adopted for an iTunes phone (such as restoring/erasing the phone and deauthorizing, then reauthorizing iTunes). However, some users have already commented that the doc's solutions aren't fixing the issue either.
Are any readers experiencing the same hiccup? If you have any thoughts on what's going on, please share your thoughts in the comments and, if you're up to the task, drop the frustrated peeps over in Apple's Discussion thread a line too. I'm sure they'll appreciate it.