I can't find the Mirage Vest

[Blind]

I'm supposed to talk to someone in Phantom Village and ride around the world on a Choboco, but he doesn't seem to be here

[Jigen Daisuke]

There's a hidden door behind the pub outside, go through the rooms, he'll be there somewhere.

[Blind]

Is it possible he disappears after beating the game?

[chaoticenigma]

Yeah, he disappears in the other versions, so that probably was kept in the Mobile. Specifically, he disappears once you get to the Phantom Village part of the final dungeon.