Mount Mirage

It may look as though Madame Pholnaset is able to cast an incredible aesthetic glamour on her chocobo, Menfeek,  but it's actually an elaborate illusion. 

Madame Pholnaset is an accomplished illusionist and aetherologist, but for her purposes casting such extreme spells on others requires knowledge about the person's weight, aether composition, vocal range if it needs tweaking, etc. This isn't a problem when it comes to Menfeek since she knows all about her feathered companion, and she's merely casting an illusion as appose to altering the chocobo's actual physical dimensions. 

There are limits though; the further away the subject the harder it is to maintain the illusion, so Madame Pholnaset usually releases the mirage once the ride is over and her pompous entrance has been made. This is especially so if the illusion is very complex.