Low-affinity transporter for external inorganic phosphate (Pi) probably involved in the acquisition of phosphate released by arbuscular mycorrhizal (AM) fungi (e.g. Gigaspora margarita and Funnelliformis mosseae) during AM symbiosis; required for propper mycorrhizal arbuscule morphology (PubMed:26476189). Acts as a Pi-sensing machinery at the root tip level, independently of AM fungi, involved in the regulation of early root branching and lateral roots formation (PubMed:26476189). NH4(+)(in) = NH4(+)(out) Present on the periarbuscular membrane in cells containing arbuscules during arbuscular mycorrhizal (AM) symbiosis with AM fungi. Expressed only in mycorrhizal roots, exclusively in cortical cells containing arbuscules, upon arbuscular mycorrhizal (AM) symbiosis with AM fungi (e.g. Gigaspora margarita and Funnelliformis mosseae) (PubMed:26476189). Also observed in root tips of non-mycorrhizal roots, in a phosphate (Pi) depended-manner, highest expression levels being observed in low Pi conditions (PubMed:26476189). Induced in roots during development of arbuscular mycorrhiza (AM) upon colonization by AM fungus (e.g. Glomeromycota intraradices, Gigaspora margarita and Funnelliformis mosseae) (PubMed:19220794, PubMed:26476189). Induced in root tips by low phosphate (Pi) levels (PubMed:26476189). Impaired phosphate (Pi) starvation induction of lateral roots formation (PubMed:26476189). Abnormal structures of arbuscular mycorrhiza (AM) fungi (e.g. Gigaspora margarita and Funnelliformis mosseae) during AM symbiosis with swollen main arbuscule trunks and reduced branching (PubMed:26476189). Lower symbiotic Pi transfer for AM fungi to the host plant (PubMed:26476189). 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.