Final answer:
The rhetorical device used in the phrase is anaphora, which emphasizes grievances by repeating 'He has' at the beginning of successive clauses to create a rhythmic structure.
Step-by-step explanation:
The rhetorical device used in the phrase 'He has plundered our seas, ravaged our coasts, burnt our towns, and destroyed the lives of our people' is anaphora. Anaphora is a literary and rhetorical device in which a word or phrase is repeated at the beginning of successive clauses or sentences. In this excerpt, the repetition of 'He has' at the beginning of each accusation emphasizes the numerous grievances and contributes to a rhythmic structure that enhances the impact of the message on the audience.