Consider the following partial differential equation:
$\style{font-family:'Times New Roman'}{3\frac{\partial^2\phi}{\partial x^2}+B\frac{\partial^2\phi}{\partial x\partial y}+3\frac{\partial^2\phi}{\partial y^2}+4\phi=0}$
For this equation to be classified as parabolic , the value of B^{2} must be _____________.