LONDON (Reuters) -British Prime Minister Boris Johnson will speak to U.S. President Joe Biden and other world leaders later on Tuesday to discuss toughening sanctions against Russia and further support for Ukraine, Johnson’s spokesman said. Leaders from Canada, France, Germany, Italy, Romania, Japan, NATO and the European Commission are also due to join the call. Earlier, a senior national security official gave Johnson and his ministers an update on Britain’s assessment of the situation in Ukraine, the spokesman said. “The next phase of the war was likely to be an attritional conflict which c…