Enables protein phosphatase binding activity; protein phosphatase inhibitor activity; and protein phosphorylated amino acid binding activity. Involved in several processes, including negative regulation of cytokine production; negative regulation of nitric oxide biosynthetic process; and negative regulation of signal transduction. Acts upstream of or within several processes, including hematopoietic progenitor cell differentiation; phagocytosis; and positive regulation of phagocytosis. Located in plasma membrane. Is expressed in several structures, including adrenal gland; cartilage; central nervous system; genitourinary system; and retina. Orthologous to human SIRPA (signal regulatory protein alpha).