The spelling of the word "sulph" has been a subject of debate for centuries. The original spelling was "sulphur" but it was later shortened to "sulfur" in American English. In British English, however, the spelling remained "sulphur" until the early 21st century when it was officially changed to "sulfur" to align with international standards. The correct pronunciation is /ˈsʌlfər/, with the stress on the first syllable and the last syllable pronounced as "fur".
Prefixes in chemical terms denoting compounds containing sulphur or sulphuric acid.
Etymological and pronouncing dictionary of the English language. By Stormonth, James, Phelp, P. H. Published 1874.