Should Phione be considerate as one of the Legendary Pokemon?
Honestly, no. It's one of the Pokémon I've never really found noticeable at all, and at times I kinda forget all about it. The fact that it's also legendary I see no sense at all in, since it doesn't really possess any of the features that are typical Pokémon, which is mostly actually strength, but you catch my drift. Together with that, I think it's the only legendary Pokémon that actually evolves, which kinda doesn't help it in this case. I don't actually know anything of its backstory either, assuming it actually has one, but as it's one of those Pokémon you aren't able to get outside of events, I really don't see why I should either.