In the context of stanza three of “Paul Revere’s Ride,” the metaphor of a "phantom ship" is used to convey an eerie and ominous presence, suggesting something ghostly or threatening. Therefore, the intended effect of the metaphor is most closely associated with:
D. To show that the British ship is dangerous.
This interpretation captures the idea of the ship as a foreboding entity in the narrative, heightening the sense of tension and danger associated with the British presence.