Yes. The developers made it so that players can access Phantom Liberty after the main story is over. This allows for a continuation of sorts in the game world. You can expect new storylines that are just as engaging as the main story, if not more in some ways. There are also new items and mechanics that are introduced in Phantom Liberty, and it's all there for you to explore regardless of whether you've already completed the main part of the game.
Definitely. Once you've wrapped up the main story, Phantom Liberty becomes available for you to play. It's like an expansion that adds new elements to the game world. There are new quests, characters, and areas to explore. So, it's a great way to continue your experience in the game even after the main plot has been concluded.