How many phenotypes are possible in ABO blood groups

4 phenotypes are possible in ABO blood groups.
The possible human phenotypes for the blood group are type A, type B, type AB, and type O.
The four main blood types are A, B, O and AB. For a blood transfusion, the ABO blood group system is used to match the blood type of the donor and the person receiving the transfusion.
Blood group A has A antigens on the red blood cells with anti-B antibodies in the plasma. Blood group B has B antigens with anti-A antibodies in the plasma. Blood group O has no antigens, but both anti-A and anti-B antibodies in the plasma. Blood group AB has both A and B antigens.