Preheat oven to 400°.
Heat a large nonstick skillet over medium-high heat. Coat pan with cooking spray. Add bell pepper and jalapeño; sauté 5 minutes. Stir in flour; remove from heat. Set aside 2 tablespoons milk. Gradually add remaining milk to pan, stirring well with a whisk. Stir in yogurt; bring to a boil. Remove from heat; stir 2 minutes or until thick. Cool 5 minutes. Stir in cheeses, salt, black pepper, and egg whites.
Working with 1 phyllo sheet at a time (cover remaining dough to keep from drying), place 2 phyllo sheets in a 13 x 9-inch baking pan coated with cooking spray; gently press sheets into bottom and sides of pan, allowing ends to extend over edges of pan. Coat top sheet with cooking spray. Fold 1 phyllo sheet in half crosswise; place on sheets in bottom of pan, and coat with cooking spray. Top with 1 phyllo sheet, gently pressing sheet into bottom and sides of pan; coat with cooking spray. Spread cheese mixture evenly over top of phyllo. Fold 1 phyllo sheet in half crosswise; gently press on cheese mixture in pan, and coat with cooking spray. Top with remaining 3 phyllo sheets, coating each sheet with cooking spray. Cut ends of sheets extending over pan. Fold edges of phyllo to form a rim; flatten rim with fork. Cut 4 slits with a sharp knife in top of phyllo; brush with reserved 2 tablespoons milk. Bake at 400° for 22 minutes. Reduce oven temperature to 375° (do not remove pie from oven); bake 20 minutes or until browned. Remove from oven; let stand 15 minutes.