Phi (/ˈfaɪ/) is a mononym derived from the Greek letter Φ (phi). It is of uncertain origin and meaning, but it may be related to the Greek word φῆν (phēn), which means "to shine" or "appear." Phi is often associated with mathematics, as it represents one of the fundamental constants in nature known as the golden ratio. This ratio, approximately equal to 1.61803, has many unique properties and appears frequently in art, architecture, and science. Despite its mathematical significance, Phi remains a rare choice for a given name, offering a distinctive option for parents seeking an unusual yet meaningful moniker.
The name Phi experienced a decline in popularity from the early to mid-1980s until the late 1980s and early 1990s, with only five births each year between 1983 and 1989. However, there was a slight resurgence in its usage in the late 1990s, with eight births recorded in 1996. Since then, the name's popularity has remained relatively stable, with five births occurring in both 1994 and 2009, totalling to 45 births over the entire period.