An experiment was conducted to evaluate the influence of a highly soluble Ca (HSC) source on performance, bone ash and mineralization, and apparent ileal digestibility of Ca, P, N, and energy in Ross 708 broiler chickens. Dietary Ca was supplied by the HSC source and monocalcium phosphate to provide 4 levels of Ca (0.45, 0.60, 0.75, or 0.90%). Available P (aP) was maintained at 0.32% in all the diets. Each diet was supplemented with 0, 500, or 2,500 U/kg of phytase as a 4 × 3 factorial. An additional diet was formulated using limestone to contain 0.90% Ca and 0.45% aP as a positive control (PC). Diets were fed to 7 replicate cages of 8 birds per cage from d 0 to 21 posthatch. Feed intake (FI) was linearly (P ≤ 0.05) reduced, and BW gain was quadratically (P ≤ 0.05) reduced as Ca from HSC increased from 0.45 to 0.90%. Phytase supplementation linearly (P ≤ 0.05) increased FI and BW gain and improved feed conversion ratio. Tibia ash and P weights were lower in birds fed 0.90% Ca from HSC compared with broilers fed 0.90% Ca from limestone. Phytase supplementation increased tibia ash and P weights in broilers fed 0.60, 0.75, or 0.90% HSC (Ca level × phytase P ≤ 0.05). Phytase supplementation linearly (P ≤ 0.05) increased tibia Ca weight. Reducing HSC from 0.90 to 0.45% or increasing phytase supplementation linearly (P ≤ 0.05) improved ileal P digestibility. Ileal Ca digestibility increased linearly only in broilers fed 0.45% Ca from HSC as phytase supplementation increased (Ca level × phytase P ≤ 0.05). Nitrogen or energy digestibility were quadratically (P ≤ 0.05) influenced as HSC or phytase increased. In conclusion, feeding HSC with phytase allowed for reductions in dietary Ca while maintaining broiler performance and bone ash. In addition, P digestibility and P in the bones were increased in broilers fed reduced dietary Ca in the presence of phytase.