Cyberpunk Phantom Liberty is an expansion to Cyberpunk 2077. It's set in the dystopian Night City. The story follows V, the protagonist, as they get entangled in a web of political intrigue, espionage, and dangerous missions. There are new characters introduced, like Songbird, who has her own complex motives and backstory. The story delves deeper into the seedy underbelly of Night City's power struggles, with V having to make tough choices that can impact the future of the city and their own survival.
One key element is the new characters, especially Songbird. She plays a crucial role in driving the story forward. Another is the political intrigue within Night City. The power struggles between different groups add a lot of depth. Also, the dangerous missions that V undertakes are key. They expose V to new areas of the city and new threats.
The main story first. You'll understand the basic world and gameplay mechanics better. It sets the foundation for everything in the game. Then, when you move on to 'phantom liberty', you can fully appreciate the new elements as an addition to what you already know.
It depends on your preference. If you want to fully immerse yourself in the rich lore and world - building of the game right away, starting with the main story might be a good choice. It gives you a broad overview of the game's setting, characters, and main conflicts.