Processes for inhibiting scale produced during wet process phosphoric acid production by adding a scale-inhibiting amount of a reagent having a primary amine-containing polymer, or salt thereof, to one or more stages of a wet process phosphoric acid production stream are provided herein, wherein the primary amine-containing polymer includes an A mer according to Formula (I): where R is H, C1-C6 alkyl, C2-C6 alkenyl, halide, or carboxyl; R1 is H, C1-C6 alkyl, or C2-C6 alkenyl; R2 is H or an A mer according to Formula (I) as herein defined; R3 is chosen from a direct bond or a C1-C12 alkyl, C2-C12 alkenyl, or a C6-C12 aryl group; and n is an integer chosen to provide a weight average molecular weight of the primary amine-containing polymer of at least 300 Daltons, and wherein the percentage of primary amines in the polymer is from 30 mole % to 100 mole % based on the total percentage of mer units in the polymer.