In the three years since Ed Zander took over as chief executive of cell-phone maker Motorola Inc., the company has gone from a troubled, overly diffuse business to a case study in corporate restructuring to a bloated technology maker badly in need of another facelift.

As billionaire investor Carl Icahn moves to increase his stake in the Schaumburg, Ill., company and prepares for a proxy fight against Motorola, doubts are mounting over whether Zander can shore up eroding profit margins and put its more than $11 billion of cash to good use.