The phrase "acted reciprocally" expresses the idea of two or more parties exchanging actions or behaviors. An antonym for this phrase could be "acted unilaterally," which means that one party acted alone, without the involvement or response of the other party. Another antonym could be "acted antagonistically," which means that the parties' actions were competitive or conflicting, rather than cooperative or mutually beneficial. "Acted independently" could also be an antonym, implying that the parties acted without coordination or collaboration. These antonyms convey different nuances of meaning and highlight the various ways in which parties can interact or fail to interact with each other.