Use a fine mesh strainer to sift two tablespoons powdered sugar judiciously over the phyllo as you make the layers. Just a bit of sugar along with the cooking spray helps them adhere to one another. Don't worry if they're loosely stacked; the crisp texture provides a nice contrast to the sautéed grapes and creamy cheese.
9 (14 x 9–inch) sheets frozen phyllo dough, thawed
2 tablespoons plus 2 teaspoons powdered sugar, divided
Place 1 phyllo sheet on a large cutting board or work surface (cover remaining dough to keep from drying). Lightly coat dough with cooking spray. Place 2 tablespoons powdered sugar in a small sieve; dust phyllo lightly with powdered sugar. Repeat procedure with 2 phyllo sheets, cooking spray, and powdered sugar, ending with powdered sugar; press layers gently to adhere. Cut phyllo stack lengthwise into 3 (3 x 14–inch) rectangles. Cut each rectangle crosswise into 4 (3 x 3 1/2–inch) rectangles to form 12 rectangles. Carefully stack 1 rectangle on top of another to form 6 stacks; press layers gently. Place stacks on a baking sheet lined with parchment paper. Repeat procedure with the remaining phyllo, cooking spray, and powdered sugar to form 18 stacks.
Cover the phyllo stacks with parchment paper; place another baking sheet on parchment. Bake at 350° for 10 minutes or until stacks are golden and crisp. Carefully remove top baking sheet and parchment. Cool phyllo stacks completely on baking sheet.
Bring port to a boil in a small saucepan over medium-high heat. Cook 10 minutes or until reduced to 1 1/2 tablespoons. Remove from heat; stir in honey and 1/8 teaspoon salt.
Melt butter in a nonstick skillet over medium-high heat. Add remaining 1/8 teaspoon salt, grapes, granulated sugar, and juice. Saute 10 minutes or until grapes are tender, stirring occasionally. Remove from heat, and cool to room temperature.
Combine cheeses in a small bowl, stirring well.
Place 1 phyllo stack on each of 6 plates, and top with 1 teaspoon cheese mixture and 1 tablespoon grape mixture. Repeat the layers once, ending with phyllo stack. Drizzle 1 teaspoon port mixture onto each plate. Sprinkle each serving with 1 teaspoon walnuts, and dust evenly with the remaining 2 teaspoons powdered sugar.