Preheat oven to 350°. Place a greased 9-in. springform pan on a double thickness of heavy-duty foil (about 18 in. square). Wrap foil securely around pan. Place on a baking sheet.
In a large bowl, whisk the butter, cream, honey, cinnamon and vanilla. Gently pull phyllo apart and add to bowl; toss to coat. Press onto bottom and up the side of prepared pan. Bake until golden brown, 40-45 minutes. Cool on a wire rack. Remove foil.
Meanwhile, in a small heavy saucepan, whisk egg yolks, sugar, mango nectar, lemon juice, cornstarch and zest until blended. Add butter; cook over medium heat, whisking constantly, until mixture comes just to a boil and is thick enough to coat a metal spoon.
Remove from heat immediately. Strain through a fine-mesh strainer into a small bowl. Stir in mango; cool. Press plastic wrap onto surface of custard. Refrigerate until cold.
Spoon filling into crust. Garnish with mandarin oranges and grapes. Remove rim from pan. Dust with confectioners' sugar.
