Likely, you'll have finished Cyberpunk 2077's main quest before diving into Dogtown and Phantom Liberty. However, if you finish the expansion first, there's some unique dialogue you'll encounter in the main game.
There are some spoilers ahead, so duck out the way if you've not yet completed either the expansion or the main game, though it is worth mentioning these aren't going to ruin the experience if you know about them beforehand.
It seems there are a few major examples of changed dialogue, with most of them focusing on AI tech V finds in Phantom Liberty. Both Anders Hellman and Alt Cunningham have unique lines of dialogue relating to the tech.
There's also a short comment from pop star Lizzy Wizzy if you wait until after the expansion to attend her concert.