"Form an extended front" is a phrase commonly used to describe spreading out or expanding a group or organization. There are numerous synonyms that can be used to convey a similar meaning, including "broaden the scope," "widen the reach," "increase the span," "enlarge the horizon," and "extend the breadth." These phrases all suggest the idea of expanding or extending the reach of a particular group or initiative. By using a variety of synonyms for "form an extended front," a writer can add color and variety to their language, while still conveying the same underlying message of growth and expansion.