There are several words that can be used as synonyms for the phrase "as proxy for." One option is "on behalf of," which means acting or speaking for someone else. Another possibility is "in lieu of," which suggests that something is being done instead of something else. "In place of" can also be used to indicate that one thing is being substituted for another. "Representing" is another synonym that works well in many contexts. Whatever word is chosen, it should convey the idea that something is being done or said on behalf of someone else or to stand in for something else.