Blend syrup, sweetener and strawberries on medium speed in blender until smooth. With blender running, gradually add cream cheese cubes; blend just until smooth. Remove from blender and gently stir in whipped topping until uniformly blended.
Pour into crust; cover.
Freeze at least 6 hours. Thaw at room temperature 15 to 30 minutes before serving. Garnish with whipped topping or fresh berries, if desired.