Why have my playlists on my iPhone disappeared?

Why have my iTunes playlists on my iPhone disappeared even though they appear when I connect the phone to iTunes on my laptop? I do not seem to be able to retrieve or reinstall them. I normally manage my music manually. Even recent CDs I imported which are showing up on iTunes on the laptop are not appearing on the iPhone. What am I doing wrong? I'm using the most recent versions of iTunes and OS software on laptop and iPhone.