Transport of phosphate groups from the cytosol to the mitochondrial matrix. Mediates salt stress tolerance through an ATP-dependent pathway and via modulation of the gibberellin metabolism. Expressed in stems, leaves and flowers. Strong expression in vascular tissues. By salt stress. Plants overexpressing MPT3/PHT3;1 display increased sensitivity to salt stress. Belongs to the mitochondrial carrier (TC 2.A.29) family. Truncated N-terminus.