also: フィー
noun
phi
The Greek letter Φ/φ, used in mathematics, physics, and engineering. Both ファイ and フィー readings are used, with ファイ being more common.
数学で、Φは黄金比を表すことが多い。
In mathematics, Φ often represents the golden ratio.
物理学では、φは磁束を表す記号として使われる。
In physics, φ is used as a symbol for magnetic flux.
Variant lowercase phi glyph; less common but still used in some fonts.
From the Greek letter Φ (phi), adopted into Japanese as a mathematical and scientific symbol. The reading ファイ comes from the Greek pronunciation, while フィー is influenced by English.