Heat oven to 375. Combine lemon juice, sugar sub., cinnamon, and almond extract in a medium bowl. Add pears and stir to coat.
Line a baking sheet with parchment. Working quickly, lay one phyllo sheet on the baking sheet, coat lightly with cooking spray, fold in half widthwise, and spray again. Repeat with remaining sheets, piling sheets in a single stack as you go.
Fold in edges 1/4 in. on each side. Lay pear slices on top of phyllo in a single layer. Bake until pears are tender and crust is golden, about 22 min. Serve warm.