Involved in cuticle formation (PubMed:10805750). May play a role in the unfolded protein response (PubMed:21199936). Catalyzes the rearrangement of -S-S- bonds in proteins. Heterotetramer of two alpha chains and two beta chains. Exist either as a phy-1(2)/pdi-2(2) tetramer, a phy-2(2)/pdi-2(2) tetramer or as a phy-1/phy-2/pdi-2(2) tetramer. Expressed in oscillating waves in hypodermal cells during the 4 larval stages and in adults. RNAi-mediated knockdown causes embryonic lethality characterized by a retraction of the fully elongated embryo, a progressive disorganization of the embryo and a failure to hatch (PubMed:10805750). Also causes increased expression of the unfolded protein response (UPR) marker hsp-4 (PubMed:21199936). Belongs to the protein disulfide isomerase family.