'phytophagial' originates from Neo-Latin/Modern scientific formation, specifically the combining element 'phytophag-' from Greek 'phytophagos', where 'phyto-' meant 'plant' and 'phagein' meant 'to eat'.

'phytophagial' developed from Greek 'phytophagos' (literally 'plant-eating'), passed into Neo-Latin as elements such as 'phytophag-' and later formed English adjectives (compare 'phytophagous'), eventually giving the modern English adjective 'phytophagial'.

Initially the root meant 'plant-eating' in Greek; over time the formation has retained this core meaning and is used in modern scientific English to describe organisms that feed on plants.