By Kate Abnett, Valerie Volcovici and Yousef Saba DUBAI (Reuters) -Countries clashed on Saturday over a possible agreement to phase-out fossil fuels at the COP28 summit in Dubai, jeopardising attempts to deliver a first-ever commitment to eventually end the use of oil and gas in 30 years of global warming talks. Saudi Arabia and Russia were among several countries insisting that the conference in Dubai focus only on reducing climate pollution – and not on targeting the fossil fuels causing it, according to observers in the negotiations. On the other side, at least 80 countries including the Un…