In less than five years, Matt's Big Breakfast has become a downtown Phoenix institution. Every day but Sunday, the diner cooks up dozens of pieces of thick peppered bacon and pounds of olive-oil crisped potatoes in a kitchen smaller than an ASU dorm room. The teeny restaurant's signature day-glow citrus counters are matched only by the warm-hearted goodness of Erenia Pool, Mrs. Matt herself. Her terminal cheerfulness can overcome even the most ardent anti-morning doldrums. Sure, her big-hearte