Phione is a blue Pokémon with a round head and a tiny body. Phione's head is crowned by a flotation sac with a long, ribbon-like antenna. Its mouth is small, and its eyes are large with blue sclerae and gray irises. Above its eyes are two blue, circular markings connected to the eyes by a thin black line. Its long, flipper-like arms have rounded tips. Phione has a red, oval gem on its chest and a single rudimentary foot spike.
Phione inflates the sac on its head to drift in the water and search for food. When the water grows warm, it will drift in packs with other members of its species. No matter how far it has drifted, it will always return to the place where it was born. Sometimes it will be seen with Manaphy, visiting the Hisui region on rare occasions. Against natural predators, it uses a defense mechanism that allows it to blend with ocean waters. Phione are known to hatch from eggs laid by Manaphy, although the relationship between the two species is still unknown.
In the Pokémon Kids: Winter Fest badge collection, all other Legendary and Mythical Pokémon have special badge borders and are obtained exclusively through either opening Master pouches or clearing timed challenges. Phione has no special border and is obtained through standard bags, in the same way all non-Legendary/Mythical Pokémon are obtained.
In the Pokémon Bank Pokédex, all other Mythical Pokémon and Special Legendary Pokémon have a shiny background, but Phione does not.
In Pokémon HOME, it is not possible to trade Mythical Pokémon via the Wonder Box, Global Trade System or Room Trade. Despite this, when HOME first launched, it was originally possible to trade Phione despite this restriction. This was fixed in a later update.
Phione is probably based on sea angels, specifically Clione. Clione are remarkably popular in Japanese documentaries, especially in Hokkaido, on which Sinnoh is based. This may also explain their appearance in Chocovine Town.
Manaphy's trait of only being able to produce Phione as offspring may be inspired by eusociality, a biological phenomenon which usually manifests in a colony of animals having a sole breeding female, or queen, tended to by her usually infertile offspring, or an example of a highly rare and unique mutation such as albinism or polydactyly. Pokédex entries, however, suggests that Manaphy are born in cold waters and are easily affected by their environment, while Phione live in warms waters and come back to their place of birth.
Phione may be a combination of Manaphy and Clione (genus of floating sea slugs).