Preheat oven to 400°F.
Stir together 1/4 cup sugar and 1/2 teaspoon five-spice powder.
Brush 1 sheet of phyllo with butter (as you work, keep remaining phyllo covered with a kitchen towel); sprinkle evenly with 1½ teaspoons sugar mixture.
Starting at one short end, fold in half to enclose butter and sugar mixture; brush top with more butter.
Transfer to a 9-inch springform pan, buttered-side-down, gently pressing into bottom and sides.
Repeat with remaining phyllo, butter and sugar mixture, arranging in overlapping layers to completely and evenly cover bottom and sides of pan.
Bake until crust is crisp and golden, 15-18 minutes.
Transfer pan to a wire rack and let cool completely. (The baked cooled crust can be wrapped and stored at room temperature up to 1 day.)
Meanwhile, in a large bowl, whisk together eggs, pumpkin, milk, syrup, vanilla, flour, salt and remaining 1/2 cup sugar and 1/2 teaspoon five-spice powder until smooth.
Pour mixture into crust and bake 20 minutes.
Reduce oven temperature to 350°F and continue baking until custard is just set in center, 40-50 minutes more.
Transfer pan to wire rack; let cool completely.
Remove pie from pan, cut into wedges and serve with whipped cream.