Effects of dietary available phosphorus (
aP
) and Ca levels and an
Escherichia coli
6-phytase supplementation were studied in Lohmann LSL-Lite hens from 25 to 37 wk of age. Eighty-four hens were used in a completely randomized design with 7 treatments. The treatments were a positive control (
PC
) diet with 0.45% aP, 3.70% Ca, and 0.16% Na from 25 to 28 wk and 0.38% aP, 3.73% Ca, and 0.15% Na from 29 to 37 wk; a negative control (
NC
) diet, similar to the PC diet, with 0.22% aP, 3.00% Ca, and 0.13% Na from 25 to 28 wk and 0.19% aP, 3.02% Ca, and 0.13% Na from 29 to 37 wk; the NC diets supplemented with phytase at 150 (NC + 150), 300 (NC + 300), 600 (NC + 600), or 1,200 (NC + 1,200) phytase unit (
FTU
)/kg; and the PC diet supplemented with phytase at 1,200 (PC + 1,200) FTU/kg. Hen performance, eggshell, and bone quality were measured on a 4-wk basis. Bone breaking strength and ash and apparent ileal digestibility (
AID
) of P and Ca were determined at 37 wk. One- and 2-way ANOVA were conducted, and Tukey's range test was used to compare multiple means where
P
≤ 0.05. No differences in hen performance, eggshell quality, bone breaking strength, bone ash, and P digestibility were observed between the PC and the NC treatments. The NC hens had lower cortical (
P
< 0.001) and trabecular + medullary bone mineral density (
P
= 0.004) and total bone mineral content (
P
< 0.001) than the PC hens. The PC + 1,200 increased cortical bone mineral density (
P
< 0.001). The reductions of aP and Ca in the NC diet were not deficient for performance but had a minor impact on bone mineralization. The NC + 600 and NC + 1,200 increased AID of P (
P
= 0.024), and all phytase treatments except the NC + 150 increased AID of Ca (
P
= 0.010) compared with the NC diet.
