It's a very very hidden big irony.
He started the movie as a jerk and egotist, with everything in his mind being about him and not caring about others. At least, on a minor, 1-person scale. We are led to believe that this perception of things being about him are wrong.
Then, as we find out after the movie ends (see wbogacz's excellent answer), the whole universe was frozen in thousands of days of a loop, all for the express purpose of providing a lesson to Phil that his initial worldview is wrong.
Except, in the end, it is all about Phil. The only mistake in the beginning that he made was the scale - the whole UNIVERSE is about him, not just an individual personal bubble of things around him.