The phantoms were such that the main characters could be walking around in the wilderness, no enemies in sight, when suddenly they're besieged out of nowhere.
They can be considered amongst the details that hurt the film, but in the same vein as Random Encounters the film tried to give reasons for a lot "taken for granted" details of Final Fantasy games that you would expect adaptations to simply not worry about: Showing the reasons why monsters don't enter cities, why the settlements are so uncommon and spread out are two details that stand out even more than the Random Encounters.
So the movie has next to nothing to do with the games its based on... the games that also have next to no real relation to each other beyond the title.
...and some kind of fantasy setting in an imaginary world. Placing your first movie adaptation in After the End Earth may not have been best move.