Place potatoes in a saucepan; cover with water. Bring to a boil. Reduce heat, and simmer 15 minutes or until tender; drain. Return potatoes to pan. Add sour cream, garlic and herb seasoning, salt, and pepper; mash mixture with a fork or potato masher until smooth. Stir in onions. Cool to room temperature.
Place 1 phyllo sheet on a large cutting board or work surface (cover remaining dough to keep from drying); layer with 2 additional phyllo sheets. Cut phyllo stack in half crosswise. Top each half with about 2 tablespoons potato mixture, leaving a 1/2-inch border. Roll up jelly-roll fashion, starting with short side. Tuck ends under; place rolls, seam sides down, on a baking sheet coated with cooking spray. Repeat with remaining phyllo and potato mixture to total 12 knishes. Lightly coat knish tops with cooking spray. Place knishes in an airtight container; freeze up to 3 months.
Preheat oven to 400°.
Place frozen knishes on a baking sheet coated with cooking spray. Bake at 400° for 25 minutes or until browned and crisp. Serve immediately.