In George Orwell's Animal Farm, the phrase "All animals are equal, but some are more equal than others" is an example of:

The correct option is b.

The phrase "All animals are equal, but some are more equal than others" is a prime example of both paradox and irony.

• A paradox is a statement that appears self-contradictory but contains a deeper truth. The idea of being "more equal" is logically impossible, as equality is an absolute state. This contradiction highlights the inherent hypocrisy and corruption of the ruling pigs.

• Irony is a literary device where there is a contrast between what is expected and what actually happens, or between what is said and what is meant. The original commandment was "All animals are equal." The altered phrase ironically undermines this ideal, revealing the pigs' manipulation and the betrayal of the revolution's principles.

• a. Symbolism involves using objects or ideas to represent something else. While Animal Farm is rich in symbolism, this specific phrase is not primarily a symbol.

• c. Hyperbole is extreme exaggeration. The phrase is not an exaggeration but a logical contradiction used to expose a truth.

• d. Metaphor is a direct comparison between two unlike things. This phrase does not make a comparison.

The final answer is $\boxed{\text{b. Paradox and irony}}$.