What is the relationship between an enlarged spleen and anemia?

Sequestration. Sometimes the body inappropriately starts chewing up your blood cells. The blood gets filtered in the spleen. The chewed up blood cells "clog the filter" in the spleen and the spleen gets enlarged.
Anemia. There is an increased risk since the spleen grabs the red blood cells and destroys them leading, to anemia, but just having an enlarged spleen does not guarantee anemia.