Combine first 3 ingredients in a small bowl, stirring well. Set aside.
Place 1 sheet of phyllo on a damp towel (keeping remaining phyllo covered). Lightly coat phyllo with cooking spray. Place remaining sheet of phyllo on top of first sheet, and lightly coat with cooking spray. Fold phyllo stack in half crosswise, bringing short ends together. Lightly coat with cooking spray. Cut phyllo stack in half crosswise, making 2 phyllo rectangles.
Spread 1 tablespoon plus 2 teaspoons sour cream mixture evenly over 1 phyllo rectangle to within 1/4 inch of edges. Place 1 ounce roast beef over sour cream mixture; top with 1 tablespoon Swiss cheese. Roll up phyllo, jellyroll fashion, starting with long side. Repeat procedure with remaining phyllo rectangle, sour cream mixture, roast beef, and cheese.
Place phyllo rolls, seam side down, on a baking sheet coated with cooking spray. Lightly coat tops of phyllo rolls with cooking spray. Bake at 375° for 15 minutes or until crisp and golden. Cut each roll in half diagonally. Serve immediately.