There are many synonyms for the phrase "form a pair." Some common ones include "couple up," "partner off," "pair off," "team up," and "unite" or "join forces." Other synonyms could include "combine," "connect," "match," "mate," "pair up," "pair together," "unite," "link," or "tie in." Alternatively, one could use phrases like "coordinate with," "pair with," "buddy up with," or "align with" instead. Using different synonyms can help to add variety, interest, and depth to one's writing, allowing for more creative expression.