In this work, a new MOF Eu-BTC-BDC-NH2 (BTC = benzene-1,3,5-tricarboxylate, BDC-NH2 = 2-aminoterephthalic acid) was synthesized by a facile and energy-efficient process, and can be utilized as a highly sensitive and selective ratiometric fluorescence probe for phosphate (Pi). The produced Eu-MOF had two emission peaks at 425 nm and 617 nm, which came from the BDC-NH2 ligand and energy transfer effect between the two ligands and Eu3+, respectively. When contact with Pi, due to the ultra-high affinity between Eu3+ and the oxygen atoms in Pi, part of the ligands were replaced and P-O-Eu bonds formed. Accordingly, the energy transfer effect was weakened, and the fluorescence intensity at 617 nm reduced, however, the peak at 425 nm increased. Based on this, a Pi ratiometric fluorescence platform with excellent performance was established with a low detection limit (LOD) of 0.07 mu M and superior selectivity for 19 common ions and 6 phosphate-containing molecules. In addition, the sensor achieved satisfactory results in the detection of environmental water samples. Finally, a portable detection kit based on hydrogel-MOFs was successfully constructed by combining with a smartphone, which can realize on-site monitoring of Pi.