Equilibrium point is $(0,0)$. Eigenvalues are $\lambda_+=-1$ and $\lambda_-=-4$ which have corresponding eigenvectors $2\choose -1$ and $1 \choose 1$ respectively. The point is a stable node.
So when sketching the diagram, there will be a line through the origin with gradient $1$ and a line through the origin with gradient $-1/2$. The arrows on these lines are going to be inwards towards the equilibrium point. How do I sketch the phase paths and isoclines?