How did the medium of Endor describe the figure she saw coming up?

Answer: An old man wearing a robe

She said, "An old man is coming up, and he is wearing a robe" (KJV: mantle). Saul knew it was Samuel and bowed down.

““Do not be afraid,” the king replied. “What do you see?” “I see a god coming up out of the earth,” the woman answered. “What does he look like?” asked Saul. “An old man is coming up,” she replied. “And he is wearing a robe.” So Saul knew that it was Samuel, and he bowed facedown in reverence.”— 1 Samuel 28:13-14 (BSB)