I have always told all my certification clients that if they ever feel it is critical to get on the ground asap they should do so, and that if they had a good reason for landing at an airport not authorized for Phase 1, that I doubt the FAA would make a fuss about it, but that lack of planning (needing fuel or a rest room) would probably not be accepted as a good excuse.
I don’t think actually declaring an emergency would necessarily be necessary, but I am not a Lawyer so do what you think is right fora specific situation.
I have had instances in the past that made me want to expedite a landing but not something I would have declared an emergency for at a class D airport.