Inorganic phosphori are widely used in food, whose quantitative detection method is of significance. This work presents a Sm-DDB (H4DDB = 1,3-di(3',5'-dicarboxylphenyl)benzene), which acts as a ratiometric fluorescence sensor to monitor PO43-, H2PO4-, and (PO3)66- with high sensitivity. The determination factors of pH, MOF dosage, and fluorescence response time are optimized as 7.35, 1 mg, and 2 min, respectively. The sensitivity tests show the linear fitting equations of I465/I598 = 0.00363·CP + 1.49183 (I465 and I598: the emission intensities at 465 and 598 nm; Cp = inorganic phosphorus concentration) for PO43-, I465/I598 = 0.00272·CP + 1.55944 for H2PO4-, and I465/I598 = 0.00957·CP + 1.55122 for (PO3)66- with LODs being 1.00 μM for PO43-, 1.33 μM for H2PO4-, and 0.38 μM for (PO3)66-. The detection method was applied in frozen shrimp, marine fish, and bacon, whose fluorescence recoveries of around 100% demonstrate its reliability. The analytical results are close to those determined by the phosphomolybdenum blue method. The Sm-DDB test paper shows an obvious emission color change, whose blue/red (B/R) values can be recognized by a smartphone APP. This work provides a smartphone-assisted visualization detection method for PO43-, H2PO4-, and (PO3)66-.