The low-level phosphorus (P) removal is increasingly becoming a challenge for P pollution control and prevention. Adsorption is a highly efficient method for achieving low-level P removal. The development of adsorbents with a strong affinity towards P and the study of limiting factors affecting low-level P removal are currently of primary importance. In this study, lanthanum carbonates (LCs) synthesized at different temperatures, designated as LC-80, LC-90 and LC-100, were compared. It was found that the synthesis temperature determined the La species and thus the ion exchange capacity, which further affected the P adsorption capacity of the LCs at low P concentrations. LC-80 and LC-90 were novel LC species (La₂O(CO₃)₂), exhibiting a higher ion exchange capacity. They combined with P through ion exchange to form inner-sphere complexes. LC-100, which was determined as LaCO₃(OH), exhibited a lower ion exchange capacity and adsorbed P anions through ion exchange and electrostatic attraction. Moreover, LC-80 and LC-90 displayed greater resistance to pH and co-existing ions, with LC-100 being more susceptible to their negative effects. A five-cycle regeneration operation demonstrated the good recyclability and reusability of LCs. In particular, LC-90 showed the highest P adsorption capacity at low P concentrations due to its strong ion exchange capacity. This remarkable performance allowed LC-90 to achieve an ultra-low P concentration at a lower cost of 283.12 $/kg P, thus making it a promising adsorbent for low-level P removal.