The phase of the Calvin cycle in which fewer ATPs of the light reaction are used is:

Explanation

The Calvin cycle has three main phases: carbon fixation, reduction, and regeneration. In the carbon fixation phase, carbon dioxide is attached to ribulose-1,5-bisphosphate with the help of the enzyme Rubisco, and no ATP is used. During the reduction phase, ATP and NADPH from the light reactions are used to convert 3-phosphoglycerate into glyceraldehyde-3-phosphate, but fewer ATP molecules are needed here. The regeneration phase then uses more ATP to rebuild ribulose-1,5-bisphosphate so the cycle can continue. Photolysis, on the other hand, is not part of the Calvin cycle; it occurs during the light reactions to split water and release oxygen. Thus, the reduction phase uses fewer ATP molecules than the other energy-requiring steps.