Final answer:
A tourniquet is used during the phlebotomy procedure to reduce blood flow.
Step-by-step explanation:
The tourniquet is used during the phlebotomy procedure to reduce blood flow. It is wrapped tightly around the patient's arm to temporarily cut off blood flow and make it easier to locate and access the vein. By reducing blood flow, the tourniquet helps to make the vein more prominent and easier to visualize during the procedure.