Answer
$(x-1)^2+(y-2)^2+(z-3)^2=14$
Work Step by Step
Because it is a sphere, the equation is of the form $(x-a)^2+(y-b)^2+(z-c)^2=r^2$.
Because the center is $ (1,2,3)$, it is of the form
$(x-1)^2+(y-2)^2+(z-3)^2=r^2$.
Because it passes through the origin, we can plug in $(0,0,0)$ and find that $r^2=14$