Using a very crude estimate;
Length of F4 fuse = 58 feet 3 inches.
Number of apparent fuselage lengths between underside of jet and ground (not taking into account viewing angle etc) seems to be approximately 3 to 4 Phantoms worth.
Therefore, altitude of number two at pull-up with burner on... between 175 and 233 feet?
Even two Phantom's worth is around 120 feet.
If so, still pretty low for such a big, loud jet...