Probable dual specificity phosphatase that binds and dephosphorylates MPK18, modulating the organization and dynamics of cortical microtubules. Acts as negative regulator of abscisic acid (ABA) signaling during seed germination and light-induced stomata aperture. H2O + O-phospho-L-seryl-[protein] = L-seryl-[protein] + phosphate H2O + O-phospho-L-threonyl-[protein] = L-threonyl-[protein] + phosphate H2O + O-phospho-L-tyrosyl-[protein] = L-tyrosyl-[protein] + phosphate Interacts with MPK18. Expressed in roots, leaves and flowers. By abscisic acid. Embryonic lethality when homozygous in the phs1-2 allele (PubMed:15208393), but after several backcrossing, phs1-2 and other homozygous alleles (phs1-4 and phs1-5) are similar to the wild-type (PubMed:20224945).