The spelling of the phrase "more impressing" is fairly straightforward using the International Phonetic Alphabet (IPA): /mɔːr ɪmˈprɛsɪŋ/. The first syllable is emphasized, and the vowel sound is long, as in "shore" or "pour." The second syllable includes a short "i" sound as in "sit" or "bit." The final syllable uses the -ing suffix and features the nasal sound of the letter "n." Overall, this phrase would be pronounced as "more im-PRESS-ing."
The term more impressing does not have a specific etymology. It appears to be a combination of the adjective impressive, meaning having a strong impact or creating admiration, and the comparative form more. The word impressive dates back to the late 16th century and derives from the Latin word impressus, which means pressed into or imprinted.