The phrase "am one of family" could be rephrased in a number of different ways using synonyms to convey the same meaning. For instance, "I belong to a family" would be a great alternative, as would "I am a member of a family" or "I am part of a family unit." Depending on the context, one could also say "I am related to a family" or "I come from a family." Other potential synonyms might include "I am kin," "I am familial," or "I am clan-based." Ultimately, the specific synonym used will depend on the speaker's goals and the tone and context of the conversation.