Final answer:
The phrase "In the vast boughs most bright" is the best example of imagery from the poem, as it paints a visually striking image of stars shining brightly within the wide branches of trees.
Step-by-step explanation:
The phrase from the poem that is the best example of imagery is "In the vast boughs most bright". Imagery is a literary device used to create a visual representation in the mind of the reader. This phrase provides a vivid picture of the bright stars situated among the expansive branches of the elm trees, tapping into the reader's senses to paint a clear and striking visual image. Compared to the other options, it evokes the strongest sensory experience, which is the essence of effective imagery.
Imagery often relies on descriptions of the environment, color, light, or other visual details to engage readers and make them feel as if they are part of the scene. Phrases such as "A rumor of the sea" and "Into infinity" suggest auditory and spatial sensations, but they do not offer the same level of concrete visual description as the chosen example. Meanwhile, "I stood a dreamer in a dream" uses metaphor to express an abstract concept, and "the stars" is too brief and lacks descriptive detail on its own.