Think Tallulah is lovely as a firstname, bit not great for a middle name.
I'm going to sound like a right knob, but IMHO, a middle name should sort of complement the firstname, not over shadow it/drown it out.
If your name is Phoebe Tallulah, I think the middle name will take centre stage.
I don't like Pheobe, it's the opposite of Tallulah..a bit wet meek and mild.
Don't listen to me, though!