Question about phi
 

What is the physical sense of phi in the momentum equation for incompressible and compressible fluids?
According to my deductions phi has relation to the components of the vector U = [u v w], so in the compressible case phi has the following physical sense in the moment equation for compressible flow:

phi = rho * u (x coordinate); phi = rho * v (y-coordinate); phi = rho * w (z-coordinate)

For the moment equation for incompressible fluid:

phi = u (x coordinate); phi = v (y-coordinate); phi = w (z-coordinate)

Because for incompressible fluid, the momentum equation is divided by density.

Is my deductions correct?