On the Neron-Severi group of surfaces with many lines

For a binary quartic form $phi$ without multiple factors, we classify the quartic K3 surfaces $phi(x,y)=phi(z,t)$ whose Neron-Severi group is (rationally) generated by lines. For generic binary forms $phi$, $psi$ of prime degree without multiple factors, we prove that the Neron-Severi group of the surface $phi(x,y)=psi(z,t)$ is rationally generated by lines.