The Greek letter (phi) is used in geometry as a constant to represent the golden ratio.
The golden ratio is a number represented by the greek letter ϕ (phi). The value of ϕ is approximately 1.618 and is a naturally occurring number in nature.
The golden rectangle is a rectangle whose width divided by height is equal to the golden number (approximately 1.618).
The Greek Alphabet is used throughout math to represent variables, constants, and coeffecients within math expressions, formulas, and equations.
The capital Greek letter Φ (capital phi).