This study reports the mechanism of reactivity of phosphate anions (HPO42−) with Ca2Al-NO3 LDH. Sequestration of PO4 by Ca2Al-NO3 was quantified by fitting the adsorption isotherm with a Langmuir model. Adsorption capacity (65.2 mgP·g−1 of LDH) is greater than the theoretical anion exchange capacity indicating further mechanism of sequestration. Partial dissolution of CaAl-NO3 results in precipitation of multiple Ca-PO4 phases. Combined characterizations by XRD, 27Al and 31P NMR, FTIR/Raman and SEM highlight the competitive precipitation of hydroxyapatite and brushite within the LDH structure. Multiple environment of PO4 anions offer promising perspective for CaAl-NO3/PO4 as slow release fertilizer.