Catalytically inactive phosphatase (PubMed:20180778, PubMed:23163895). By binding to G3BP1, inhibits the formation of G3BP1- induced stress granules (PubMed:20180778, PubMed:23163895). Does not act by protecting the dephosphorylation of G3BP1 at 'Ser-149' (PubMed:23163895). Inhibits PTPMT1 phosphatase activity (PubMed:24709986). By inhibiting PTPMT1, positively regulates intrinsic apoptosis (PubMed:21262771). May play a role in the formation of neurites during neuronal development (PubMed:29250526). {ECO:0000269|PubMed:20180778, ECO:0000269|PubMed:21262771, ECO:0000269|PubMed:23163895, ECO:0000269|PubMed:24709986, ECO:0000269|PubMed:29250526}. This is the function of STYXL1 (serine/threonine/tyrosine interacting like 1, ENSG00000127952).