U+03C6 "φ" Greek Small Letter Phi Unicode Character

U+03C6 "φ" Greek Small Letter Phi is the twenty first letter of the Greek alphabet, representing an aspirated voiceless bilabial or labiodental fricative sound in Ancient Greek and a voiceless labiodental fricative in Modern Greek. In mathematics and science, it is widely used as a symbol for the golden ratio (approximately 1.618), the Euler totient function in number theory, and magnetic flux in physics, as well as representing a phase angle in engineering and a null set in set theory. Its visual form typically resembles a circle with a vertical line through it, though a cursive variant (ϕ) is also common in technical contexts.