Flame retardant flexible polyurethane foam compositions, methods of flame retarding flexible polyurethane foam compositions, articles made therefrom and flame retardants that comprise blends of (alkyl substituted) triaryl phosphate ester and phosphorus-containing flame retardant having at least about 5 wt. % phosphorus additives. The combined weight of the (alkyl substituted) triaryl phosphate ester and the phosphorus-containing flame retardant comprises about 5 to about 40% by weight of the flexible polyurethane foam compositions or reaction mixtures. The ratio of the (alkyl substituted) triaryl phosphate ester to the phosphorus-containing flame retardant is from about 95:5 to about 50:50 percent by weight.