What is a word for referring to the sound of a word?

The word you're looking for is "phonetic."

When we refer to the sound of a word or how it's pronounced, we're talking about its phonetic qualities. This term comes from phonetics, which is the study of speech sounds and how they’re produced and heard. So if you're describing the sound of a word, you're describing its phonetic aspects.

Another term that might come in handy is "onomatopoeia," which specifically refers to words that imitate sounds, like "buzz," "clang," or "whisper."