Make whipped cream: Beat heavy cream (and cream cheese if using) on medium speed until it begins to thicken. Add powdered sugar and vanilla. Beat to stiff peaks. Do not overbeat.
Assemble: In a large glass trifle bowl or clear serving bowl, layer: — A generous layer of angel food cake pieces (bottom) — A thick layer of whipped cream — A layer of sliced strawberries and some blueberries. Repeat layers once more.
Finish top: Arrange remaining strawberries and blueberries decoratively on top. For a flag effect, cluster blueberries in the upper left and arrange strawberry slices in rows across the rest.
Chill: Cover and refrigerate at least 2 hours before serving (overnight is better — the cake softens beautifully).