Exhibits phosphatidylglycerophosphate phosphatase activity (PubMed:29476828). Involved in root growth and columella cells organization (PubMed:29476828). May possess protein phosphatase activity (By similarity). 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 1,2-diacyl-sn-glycero-3-phospho-(1'-sn-glycero-3'-phosphate) + H2O = 1,2-diacyl-sn-glycero-3-phospho-(1'-sn-glycerol) + phosphate Phospholipid metabolism; phosphatidylglycerol biosynthesis; phosphatidylglycerol from CDP-diacylglycerol: step 2/2. Expressed in roots, leaves, stems and flowers. Expressed at low levels in stems and flowers. No visible phenotype in the double mutant ptpmt1-1 ptpmt2-1 (PubMed:29476828). But plants lacking PTPMT1, PTPMT2 and PGPP1 have strongly shorter roots associated with a defective order of columella cells in the root apices, with stronger effect than in the single mutant pgpp1-1 (PubMed:29476828). Belongs to the protein-tyrosine phosphatase family. Non-receptor class dual specificity subfamily.