How we can localize sound vertically (up-down) and front-to-back?
The Wikipedia article is quite good.

In brief, as you state, the wave phase can be used only to localise sounds in the plane of the ears. To have an approximation of the position in the median plane (above-below/front-back), we use asymmetries that distort the sound differently at different frequencies. 

In humans, it seems that these asymmetries and their processing are not genetically programmed but evolved by each listener.

This is different in owls, although different species have each a specific asymmetry. https://en.wikipedia.org/wiki/Sound_localization_in_owls