Reinforcements led by William Phillips ( who served under Burgoyne at Saratoga ) arrived in late March , and Phillips led further raids across Virginia , including a defeat of Baron von Steuben at Petersburg , until his death of fever on 12 May 1781 . Reinforcements led by William Phillips ( who served under Burgoyne at Saratoga ) arrived in late March , and Phillips led further raids across Virginia , including a defeat of Baron von Steuben at Petersburg , until his death of fever on May 12 , 1781 .