Cook bacon in a large skillet until crisp; remove bacon, and drain on paper towels, reserving 2 tablespoons drippings in skillet. Set bacon aside.
Sauté yellow and green onions in hot drippings in skillet over medium-high heat 5 minutes or until tender. Add garlic; sauté 1 minute.
Scoop out potato pulp, and place in a large bowl. Add sour cream, and mash with a potato masher. Stir in onion mixture, 1/2 cup butter, bacon, salt, pepper, and soy sauce.
Brush thawed phyllo sheets with 1/2 cup melted butter. Arrange 5 sheets on bottom of a lightly greased 11- x 15-inch jellyroll pan. Spread with potato mixture; top with remaining 5 phyllo sheets.
Bake at 350° for 25 to 30 minutes or until golden. Cut into squares before serving; garnish, if desired.
* 1 (22-ounce) package frozen mashed potatoes may be substituted for baked potato pulp. Cook according to package directions.