PhD interview - short (!) presentation
Definitely don't try to cover everything. This is certainly not expected, and as you noted, is just not possible in a limited amount of time. What they likely would want to see is if you can explain the main points of your research in a succint way. Trying to cover too much will force you to rush trhough the material, making it difficult to follow. You can still show that you master a subject without getting into all the technical details. Indeed, it takes a good understanding of a research problem/project to be able to place it into perspective, to explain the main motivations and the most important results.

So what should be in the presentation? Different people will give different advice, but I think the following guidelines are sensible. First of all, you should identify the one or two main results of your research. Make sure that you have enough time to cover them, for example by addressing the main points in the beginning of your talk. You can go into the details (such as the methods you used) later on. Another important item is the motivation behind the research. Why did you research this particular problem, and why should people care about it? This might also be a good point to briefly mention the state of the art of the field, and explain how your work extends this. Towards the end of your talk you could go more into the technical details, but take into account that most of your audience may not be an expert on your topic.

And finally, make sure you practice your talk a few times. Ask a few more experienced people whom you trust (and can give good feedback) to attend a practice talk to give suggestions on how your presentation can be improved. Don't worry if it seems like you would have to redo the entire thing: this will only make it better.