I’d say hyperbole. Hyperbole is an exaggeration, and “importance” is being “earnest”. It’s like saying it twice. It’s meant to seem big and important. The others do not seem to fit the description of that phrase.
Pun Simile- Figure of speech in which one thing is compared to another. (a pun simile is used in a humorous way, usually)
Metaphor An analogy between two objects or ideas, conveyed by the use of a word instead of another.
Oxymoron- a figure of speech in which apparently contradictory terms appear in conjunction.