Okay so matrix T(x)=x2 and with respect to the basis {1,x,x²,x³} the second column would be (0,0,1,0), T(x2)=x3 and with respect to the basis {1,x,x²,x³} would be (0,0,0,1).
I would then say that
T=(0 0 0)
(1 0 0)
(0 1 0)
(0 0 1)
with respect to {1,x,x²,x³} right? Not with respect...