phylum n.

before vowels phyl-, modern word-forming element, mostly in the sciences, often meaning "phylum," from Greek phylon, phylē "a tribe," also a political subdivision in ancient Athens, from base of phyein "to bring forth, produce, make to grow," whence also physis "nature" (from PIE root *bheue- "to be, exist, grow").

*bheuə-, also *bheu-, Proto-Indo-European root meaning "to be, exist, grow."

It forms all or part of: Bauhaus; be; beam; Boer; bondage; boodle; boom (n.1) "long pole;" boor; booth; bound (adj.2) "ready to go;" bower; bowery; build; bumpkin; busk; bustle (v.) "be active;" byre; bylaw; Eisteddfod; Euphues; fiat; forebear; future; husband; imp; Monophysite; neighbor; neophyte; phyletic; phylo-; phylum; phylogeny; physic; physico-; physics; physio-; physique; -phyte; phyto-; symphysis.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit bhavah "becoming," bhavati "becomes, happens," bhumih "earth, world;" Greek phyein "to bring forth, make grow," phytos, phyton "a plant," physis "growth, nature," phylon "tribe, class, race," phyle "tribe, clan;" Old English beon "be, exist, come to be, become, happen;" Old Church Slavonic byti "be," Greek phu- "become," Old Irish bi'u "I am," Lithuanian būti "to be," Russian byt' "to be."