In The Moment of Zuke: Critical Positions and Pivotal Decisions for Colle System Players, David Rudel wrote that the main line of the c3-Colle was looking quite grim for White.
He proposed that Colle-Koltanowski players should adopt a new idea, meeting 1.d4 d5 2.Nf3 Nf6 3.e3 e6 4.Bd3 c5 5.c3 Nc6 6.Nbd2 Bd6 7.O-O O-O with 8.dxc5 Bxc5 9.b4!, a variation he dubbed the Koltanowski-Phoenix Attack.
Rudel promised to write a treatise on this new idea, and - two years later - he has delivered.
Koltanowski Phoenix Attack: The future of the c3-Colle is a 250+ page project giving extensive coverage of all critical defenses.
Even though the book is long, it is organized in such a way that a player can begin playing the Koltanowski-Phoenix almost immediately. Rudel first gives a "Simple mini-Repertoire" that can be learned in hours, and then he provides more complicated, alternate lines that can be added as the player becomes more experienced with the opening.
David Rudel is an authority on the Colle System, Koltanowski-Phoenix Attack: The Future of the c3-Colle being his third book intended for Colle System players.