Moon phases at birth
On the day you were born the Moon stood a certain distance from the Sun, and that distance says something your Sun sign alone does not. Your birth lunar phase is not a reading of the Moon on its own: it is the relationship between the two lights, the angle between them, from 0 degrees at the New Moon to 180 at the Full Moon.
Your solar birthday points to an underlying direction, the reason you move at all. The lunar phase describes the manner: how you actually handle the problems of daily life and of relationships, how you make what you are aiming at workable day by day.
The cycle falls into two halves. In the first, from New Moon to Full Moon, the dominant work is building: giving shape to new structures, taking initiative, standing out as an individual. In the second, from Full Moon to the next New Moon, the dominant work is making sense: understanding what all that building means, passing it on, and where necessary taking apart the shells that no longer answer. Eight phases cover the whole turn, each with its own task.
There is a very concrete side to this too. Every month, looking at the Moon in the sky, you can spot when it returns to the phase it held at your birth. That is your lunation birthday, an appointment you can keep with the naked eye and no calculation, and it lets you feel the rhythm you have carried from the start.