$\phi$ — Phi

Lowercase phi (Φ, often written φ) denotes magnetic flux — the amount of magnetic field passing through an area — and also phase angle in waves and oscillations. Uppercase Φ is standard for flux.

SI unit: Wb (weber, as magnetic flux)

Used in

• Magnetic flux Φ = BAcosθ
• Faraday's law EMF = −dΦ/dt
• Phase in wave equations