  The non-zero Dirac phases $\delta^q$ and $\delta^l$ in the CKM and PMNS
mixing matrices signify CP violation. In general they are independent.
Experimental data including recent T2K results show, however, that in the
original KM parameterization for the mixing matrix, the sum $\delta^q_{\rm KM}
+ \delta^l_{\rm KM}$ is close to zero with $\delta^q_{\rm KM}$ to be
approximately $\pi/2$. The KM parameterization may have provided some hints
that these phases are actually related and CP is maximally violated. We show
that this sum rule can be accommodated in models with spontaneous CP violation
where both phases originate from a non-trivial common spontaneous CP violating
maximized phase in the Higgs potential. We find some interesting
phenomenological consequences for flavor changing neutral current and CP
violation for such a model. In particular, data from $B_s - \bar B_s$ mixing
provide very strong constraints on the mass scale for the new neutral scalars
in the model, yet the model still allows the electric dipole moments of
electron and neutron to reach to their current upper bounds. The model can be
tested by near future experiments.
