Philip's clothing changes three times during his date to the opera with Allegra. When they leave for the opera, he is seen wearing jeans, a sweater and a suit jacket. Immediately after the opera, he is wearing a button-up shirt and khakis instead of his sweater and jeans. During dinner, Philip is seen wearing the sweater with the khakis while his jacket is hanging over the back of his chair.
At approximately 9:15 into the film, there is a scene in which Allegra is barefoot conversing with Molly while laying on a bed. Allegra does not move, but her mirrored reflection shows that her leg briefly changes position, from sitting with her legs out, to crossed legged for a brief shot, then back to legs out, without her ever moving.
If you look really close during the first sex scene between Philip and Allegra, you can see Philip's underwear.