Final answer:
The phlebotomist should ask the patient to apply pressure, release the tourniquet, and stop the draw. Then, they should assess the situation and call for a nurse if needed.
Step-by-step explanation:
When a phlebotomist observes a hematoma developing at the site of a venous blood draw, the appropriate action to take is to ask the patient to apply pressure to the area. If the hematoma is minor, the phlebotomist can ask the patient to maintain pressure on the site to help stop the bleeding and prevent the hematoma from worsening. However, if the situation seems more serious, the phlebotomist should release the tourniquet immediately to reduce further injury, stop the draw, and assess the patient's condition. If necessary, they should escalate the situation by calling for a nurse or other healthcare professional to ensure proper care and intervention.