How do we get Phi?

Just like Pi, Phi is a product of pure geometry.
It is intrinsically related to the number 5.

Starting with a square of length 1 and double it, we got root5 from simple Pythagoras equation h^2=a^2 + b^2.
Rotating this line we see how phi is resolved.
phi=root5/2 +1/2

We find that the 5 pointed star, or pentagram, is defined by the phi proportions.