Low-affinity transporter for external inorganic phosphate (Pi) that may be involved in the acquisition of phosphate released by arbuscular mycorrhizal (AM) fungi (e.g. Glomus versiforme and G.intraradices) during AM symbiosis; not required for mycorrhizal arbuscule development. NH4(+)(in) = NH4(+)(out) Present on the periarbuscular membrane in cells containing arbuscules during arbuscular mycorrhizal (AM) symbiosis with AM fungi. During arbuscular mycorrhizal (AM) symbiosis with AM fungi, accumulates exclusively in cortical cells harboring arbuscules. Accumulates in roots during colonization by arbuscular mycorrhizal (AM) fungi (e.g. Glomus versiforme). Normal arbuscular mycorrhizal (AM) symbiosis with AM fungi (PubMed:25841038). Plants missing both PT4 and PT8 fail to establish AM symbiosis with AM fungi in high nitrogen conditions, leading to premature arbuscule degeneration (PAD); these phenotypes are suppressed in nitrogen-deprived conditions in an AMT2-3-dependent manner (PubMed:25841038). Although related to the sugar transporter family, it does not transport sugars. Belongs to the major facilitator superfamily. phosphate:H(+) symporter (TC 2.A.1.9) family.