Final answer:
A phlebotomist should use an EDTA tube for a CBC test to prevent blood clotting and preserve blood cell integrity, essential for accurate results.
Step-by-step explanation:
A phlebotomist should select an EDTA tube when collecting a blood specimen for a 'Complete Blood Count (CBC)'. The EDTA acts as an anticoagulant to prevent blood clotting and preserve the shape of cells and their constituents, which is essential for an accurate CBC analysis. Using the correct tube is critical to ensure the validity of the CBC results, which measure the levels of red blood cells, white blood cells, platelets, hemoglobin, and other blood components.