Final answer:
The most common vein for routine phlebotomy is the median cubital vein.
Step-by-step explanation:
The most common vein for routine phlebotomy is the median cubital vein. It is a superficial vessel located in the antecubital region that links the cephalic vein to the basilic vein in the form of a 'V'. The median cubital vein is frequently chosen as it is easily accessible and provides a good flow of blood for collection.