The invention provides variant phytase enzymes having increased thermal stability relative to their counterpart parent enzymes. The modifications to the enzymes include both single substitutions and various combinations of substitutions that provide improved stability and activity. The invention further provides nucleic acids encoding the variant phytase enzymes, host cells and vectors containing and expressing them, as well as feed compositions useful for providing improved nutrition, particularly with respect to the bioavailability of dietary phosphate, calcium, iron and zinc, among others.