The final phase for the painting would be the adjustment phase, which basically is the fine tuning of the painting after completing the color phase. Most of the heavy lifting should have been done in the underpainting phase.
Ironically, the final adjustments actually took longer than the color phase, probably because as the artist you may never really feel that the painting is ever complete. But there is the point where you end up over painting, which is also the point where you want to stop.
First focus here is to emphasis the cooler planes so that the planes that are supposed to recede back into the background are doing just that. Then, there should be some further emphasis on the light effect to ensure that the viewer knows where the light hits the face.
Also, some additional work was done to the background to ensure that it is knocked back and remains the background, so that it does not interfere with the main subject of the painting.
Some additional work was done in the eye area, but that may not show up in the scan. Some more tweaks to the hair to make it look more lively, and additional work was applied to the creases within the shirt of the subject.
After some other minor tweaking, the final result is the painting that you see below.