Macrophilia is an attraction to giants, giantesses, or other people who are similarly huge compared to the average height. (This can be mere interest, or it can be sexual attraction.)
The reverse of macrophilia can be called microphilia, but that word is often reserved to things small compared to the average height (as opposed to what's small from the giant's perspective). Macrophilia in general can refer to any relationship with a large difference in scale.
Common macrophile motifs are the Godzilla-style destruction of cities, vorarephilia, and fascination with certain body parts writ large (such as the feet, among other things).
From Greek μακρος + φιλια, roughly 'love of large things'.