What were the reasons behind Biden's call to Putin?

Joe Biden's call to Vladimir Putin on Tuesday, April 13, was prompted by Moscow's reaction to the crisis in the Donbass. The Americans are trying to tame Putin with  carrots and sticks. Biden called Putin after Shoygu's speech The US President was advised to call the Russian leader not to have Ukraine reformatted as a result of Russia's response to the escalation in the Donbass. It appears that Biden called Putin following the statements from Russian Defense Minister Sergei Shoygu, who announced the redeployment of two armies and three airborne units to the western borders of Russia in three weeks. The statement that the US administration released following the telephone conversation, said that Biden asked (did not demand!) the Russian president to ease tensions with regard to Ukraine. Biden also stressed out the unwavering commitment of the United States to the sovereignty and territorial integrity of Ukraine. In fact, this is about nothing from the point of view of Realpolitik.