Screenshot of Phalanx UI
Phalanx is an aesthetic interface modification that adds another hotbar underneath the original. It does this while still trying to look like a genuine part of the original hotbar design.
This second hotbar mirrors one of the floating hotbars. In practical terms, this means one of the floating hotbars was made static and moved to form the second row of the hotbar.
The second floating hotbar will retain all its original functionality.