2600: Sulfur & Sulphur: Why the Difference Jan 27, 2021

British English spelling tends to represent the more traditional version, but not always. The 'PH' in 'sulphur' has no basis in English. Usually, a 'PH' to represent the [f] means that it was spelt with a φ (Phi) in Greek, but 'sulfur' is not from Greek. Moreover, the spelling in Latin or French where English adopted this spelling is also not with a 'PH'. This is where the American English spelling comes from, with the British spelling being a result of a later insert.