Phagocytosis means engulfing and ingesting foreign stuff by phagocytes. And a macrophage is a phagocyte.
Macrophages are key in the battle against infectious disease pathogens, like bacteria and viruses. A macrophage engulfs substances, e.g. antigens, that may otherwise participate in a blossoming infection.
A macrophage does not travel about, but instead stands guard in one part of your body. Macrophages are found in many organs and tissues, such as your liver, spleen, lymph nodes, tonsils, connective tissue, brain, breast tissue, lungs and skin.
Macrophages are believed to be involved in the inflammatory disease process, e.g. rheumatoid arthritis, and metastasis of cancer as well. Research thus far seems to indicate their involvement may be contrary to the maintenance of good health.