The answer
"The glory of God" is a phrase commonly used to denote the visible symbols of God. It means some magnificent representation; a splendor, or light that is the appropriate exhibition of the presence of God. "For the Son of Man will come in the glory of His Father with His angels, and then He will reward each according to his works" (Matthew 16:27)."The glory of God" here means an exceedingly great or bright luminous appearance perhaps not unlike what St. Paul saw on the way to Damascus. So the representation of the Father and the Son does not mean that St. Stephen saw the two in a human form but that he saw only the Lord Jesus Christ, being the Son of man, having taken our nature and being there clothed with a glorious body and saw God as a light.
Answered by His Eminence Metropolitan Youssef (opens in a new tab)