The dock itself has the footprint of a smartphone, though thicker. The 100 watt power brick is large, as large as that of a big laptop. It has to be that way because the Anker dock supports up to 85 watts for laptop charging. And the latter is where the “mostly” comes in.
https://www.amazon.com/Anker-PowerExpand-Thunderbolt-Charging-Display/dp/B08RYZJY8M