It's a substance inside of some plastics that makes them more pliable and has been linked, and not linked, to various medical issues. Most medical journal's I've read(mind you less than 10), have all come to the conclusion that they don't really know how it affects things.
http://en.wikipedia.org/wiki/Phthalates and yes, I know wikipedia shouldn't be used for science stuff, but it's good for quick summaries as long as you check references