Among the architects and engineers associated with the influential, midcentury group known as the Philadelphia School, Louis Kahn and Robert Venturi are easily the most famous. But Robert Geddes, who died Monday at 99, was the group’s heart and soul, the architect who most exemplified the Philadelphia School’s ideals, and the one most committed to reconciling modernist design principles with traditional urban values. His work was proof that you could insert bold buildings into cities without dismantling the things around them.