Yea I agree with Vaibabe here, mine have all been around the 250-350 word mark. Never as much as 3 sides, so you've got plenty of space. Think of it as prep for your thesis abstract, you will have to be able to distill the key points of your PhD into a few sentences at the end anyway! Just put down the key reasons your research is necessary, what the methods used were, your main results and the implications of these. And it's just the most important and interesting information you want to include, especially if it's for a presentation abstract.