OK.
Every prophet sees this before receiving a prophecy or message from God. The Shekhinah, the settling of the Divine presence.. Since God has no visible shape or material form what he saw was the means by which God got his attention to speak to his mind as angels are messengers of God.
At first, from a distance, Moses saw a burning bush. When he got closer he only heard God speak.
Actually, Moses saw the Lord. In Exodus 3:16, "Go, and gather the elders of Israel together, and say unto them, The Lord God of your fathers, the God of Abraham, of Isaac, and of Jacob, APPEARED unto me (Moses) saying, I have surely visited you, and seen that which is done to you in Egypt." Earlier in the chapter, verse 6, "Moses hid his face; for he was afraid to look upon God." If he would have looked, in which he eventually did, he would have seen him. It's man's construct that God does not have a body to see, hear or smell. But, that is false. If that was true, the God of Moses would have been an idol which can't see, hear or smell. So, Moses didn't only hear the voice of God, he saw the God of Israel.
Something else, we know that the God of Moses, was Jehovah. In verse 16 it also points out that this God is the God of Abraham, Isaac and Jacob specifically. And, in Genesis 3:22, The Lord God said , Behold, the man is become as one of US..." The Lord God that Moses saw was therefore the Son of the Father God. This logical conclusion is supported with Jesus saying in John 10:34 that "Jesus answered them, Is it not written in your law, I SAID, ye are gods?" He was referring to when he told the author of Psalms 82:6 that Jesus was the same Lord, Jehovah. Jehovah is not the Father. He is the Son. Elohim is the Father. The Most High God is not Jehovah. Critical error by most scholars especially Jehovah Witnesses...