Yeah, about 40 years. It only was above 2 million in 1950 and '60, slid to 1.9 mil in '70 and has lost 400k+ since. But the problem with all of these population comparisons is the issue of "area." Philly is only about 135 square miles, Phoenix is 475 sq mi. Phoenix would have to grow to over 5 million to be equal in density, and I find it doubtful it ever will grow that large (especially over the issue of water. There's too damn many people in a lot of those places out west as it is).