A solid phosphite composite, having at least a portion in amorphous form, which includes at least one, preferably two or more phosphite antioxidants or alternatively at least one phosphite and at least one other polymer additive. The phosphites, at least one of which can initially be a liquid, are generally uniformly distributed since they are melt blended. A desired class of phosphites are the bis(arylalkylphenyl)pentaerythritol diphosphites, at least a portion of which is in amorphous form.