Show that $\phi : \mathbb{R}^2 \rightarrow \mathbb{R}^2$ given by $\phi(x,y) = (x,x+y)$ is linear 

I know that to be linear it must satisfy:

(i) $\phi(x+y) = \phi(x) + \phi(y)$, and

(ii) $\phi(ax) = a\phi(x)$

But, how does one apply that to the given values above?