The Schlick Phase Function node is connected to the Phase input of a ScatteringDefines how fast light gets scattered when traveling through the medium. or Volume MediumA shading system designed to render volumes such as smoke and fog., to control the scattering direction.
Scattering Direction - Controls light direction as it scatters through the surface. A value of 0 results in light scattering equally in all directions; a positive value results in forward scattering, where photons continue the same approximate direction as when they enter the surface; and a negative value results in backwards scattering, where light moves through the surface in the same direction, but opposite to the angle that they entered the surface. This is known as backscattering.