Not to be confused with the Phong Reflectance Model, Phong Shading yields more accurate results than Gouraud shading but does not work well in the rendering pipeline.
Rather than interpolating colors between vertices, Phong shading requires that the normals at the vertices be interpolated and the interpolated normals be used in the Phong reflectance equation.
This will pick up specular reflections that Gouraud shading misses, but requires normals to be computed essentially at each pixel rather than at each vertex.