At Rephidim, who led Israel's men in battle against the Amalekites?

Answer: Joshua

Moses said to Joshua, 'Choose some of our men and go out to fight the Amalekites.'

“So Moses said to Joshua, “Choose some of our men and go out to fight the Amalekites. Tomorrow I will stand on the hilltop with the staff of God in my hand.””— Exodus 17:9 (BSB)