By respiratory system we usually mean the passages that transport incoming air to the lungs and to the microscopic air sacs called alveoli where gases are exchanged. The term respiration refers to the whole chain of processes from the inhalation of air to the use of oxygen in the cells. Index. Reference.
Phagocytes are the white blood cells that protect the body by eating (phagocytosing) dirt, bacteria and dead or dying cells. They are important for fighting infections. They are also important for becoming immune. Phagocytes are important in all animals and are very complex in vertebrates.
Function is to phagocytosis dead or damaged cells, certain bacteria, and fungi; precursor to macrophages and osteoclasts; also cooperate with lymphocytes in the immune system as APCs