"Backing the salt mines" is a phrase used to describe hard work or manual labour, particularly in reference to the mining industry. The spelling of "backing" may seem unusual, but it is actually a variant of the word "breaking" in this context. The IPA phonetic transcription for "backing" is /ˈbækɪŋ/, while "salt mines" is simply /sɔlt maɪnz/. Overall, this phrase paints a vivid picture of the laborious nature of mining work, and its spelling reflects the unique language used in specific industries.