Final answer:
The phrase "According to Branch Rickey" is the attribution in the text, as it credits the source of information.
Step-by-step explanation:
The phrase that serves as an attribution in the text is "According to Branch Rickey". An attribution is used to indicate the source of information, giving credit to the person who provided it or is responsible for it. In the context provided, the phrase clearly identifies Branch Rickey as the source or subject of the information being discussed, in this case, related to the acquisition of Jackie Robinson by the Brooklyn Dodgers and the broader topic of the integration of baseball.