Protein phosphatase component of the sperm flagellar doublet microtubules (By similarity). May act as a regulator of sperm motility by mediating dephosphorylation of sperm doublet microtubule proteins (By similarity). Can dephosphorylate single and diphosphorylated synthetic MAPK peptides, with preference for the phosphotyrosine and diphosphorylated forms over phosphothreonine (By similarity). . This is the function of ENSG00000189037 (DUSP21, dual specificity phosphatase 21).