A 2 × 2 factorial design experiment examined the effect of dietary non-phytate phosphorus (NPP) (1.3 and 4.0 g/kg) and 3-phytase (F) (0 and 150 FTU/kg) on the performance indicators of hens, physical parameters of eggs, phosphorus (P) content of the eggshells, and the pH of the digestive tract of laying hens. Two hundred and forty hens (ISA Brown) were housed in enriched cages and fed a wheat-maize-based diet. A significant effect of both NPP and F was found for the yolk colour (P = 0.016) and shell thickness (P = 0.038). The F supplement or higher level of NPP alone and in combination increased the value of the yolk colour and shell thickness. The supplementation of the basal diet with F significantly increased the laying performance, especially with regard to the egg weight and feed conversion ratio. The higher dose of NPP had a negative effect on the egg production, feed intake, and feed conversion ratio. The lower level of NPP (1.3 g/kg) decreased the internal egg quality and shell quality, except for the shell strength. In contrast, the addition of 3-phytase to the diet increased the shell thickness and shell weight. The P content in the eggshells was not influenced by the dietary treatment. The higher level of NPP or F increased the pH in the gizzard to a value suitable for F activity. The hens fed a diet containing 1.3 g/kg NPP achieved a higher performance; moreover, the F supplement at 150 FTU/kg increased the external quality of the eggs.