wt of the total weight of the reactants there is no particular limitation to reaction conditions for the condensation reaction a reaction temperature is preferably above 90 u00b0 c and the reaction time is preferably longer than 2 hours it should be understood that the reaction conditions may be modulated according to practical requirements the present invention also provides a method for preparing the phosphorus containing compound represented by formula i including the steps of 1 performing an addition reaction for an aryl aldehyde compound with an organic cyclic phosphorus compound represented by formula ii to form a phosphorus containing compound having an alcohol group wherein an amount of the aryl aldehyde compound used is 0 7 to 1 3 mol with respect to 1 mol of the organic cyclic phosphorus compound represented by formula ii and 2 performing a condensation reaction for the phosphorus containing compound having an alcohol group obtained from the addition reaction with an aryl compound at least having a substituent of u2014 oh u2014 cooh u2014 nh 2 u2014 cho u2014 sh u2014 so 3 h u2014 conh 2 u2014 nhcoor 4 or anhydride wherein an amount of the aryl compound used for the condensation reaction is greater than 0 8 mol with respect to 1 mol of the obtained phosphorus containing compound having an alcohol group the invention can be more fully understood by reading the following examples which should not set any restriction to the scope embraced.