Why is Joseph not listed among the twelve tribes around the tabernacle?
Joseph is omitted because his two sons, Manasseh and Ephraim, become the two half-tribes that take his place among the twelve stationed around the tabernacle. Levi is also absent as the priestly tribe, so the perimeter arrangement counts the two half-tribes in Joseph's stead.
Les explains that when the tribes came out and were stationed around the tabernacle, Joseph is not listed. Joseph had been among the twelve, but Manasseh and Ephraim, Joseph's two sons, are called the two half-tribes and take his place/share. That accounts for the twelve around the perimeter. Levi is also left out because Levi was the priestly tribe, and later in the Promised Land Levi did not have an inheritance. They had a central area around Jerusalem for the priests to live and were supported by what came from the other tribes, much like God's servants today depend on offerings, tithes, and gifts.