Of course he should. If you can't call racism racism, if you can't call antisemitism antisemitism, and if you can't call Islamophobia Islamophobia, then how are we going to fix it?
Notes from Wikiquote
Asked if the prime minister should condemn the comments of the former Conservative deputy chairman Lee Anderson, who had lost the parliamentary whip for claiming the London Mayor, Sadiq Khan, is controlled by Islamists.