Spoilers included
The more I think about Phantom Thread, the more I’m impressed with the simplicity and subtlety of the love story. It breaks down to this: she loves him and knows he needs to relax, but he can’t. She sees he builds up to a state of fevered intensity and then maybe crashes. She tries to help him but he resists, so she resorts to a rather strange remedy. It works. The key moment is when he sees the image of his mother in the wedding dress he made for her: she has replaced his mother as the one person other than his sister who truly cares for him. She takes this to what is, in the movie, a necessary extreme. And when he realizes this, then he recognizes how much she truly loves him and he gives himself over to her as she has given herself over to him. It’s a love story.