  Several approximate equalities among the matrix elements of CKM and PMNS
imply that hidden symmetries may exist and be common for both quark and
neutrino sectors. The CP phase of the CKM matrix ($\delta_{\rm CKM}$) is
involved in these equalities and can be investigated when these equalities turn
into several equations. As we substitute those experimentally measured values
of the three mixing angles into the equations for quarks, it is noted that one
of the equations which holds exactly has a solution $\delta_{\rm
CKM}=68.95^\circ$. That value accords with $(69.1^{+2.02}_{-3.85})^\circ$
determined from available data. Generalizing the scenario to the lepton sector,
the same equality determines the leptonic CP phase $\delta_{\rm PMNS}$ to be $
276.10^\circ$. Thus we predict the value of $\delta_{\rm PMNS}$ from the
equation. So far there is no direct measurement on $\delta_{\rm PMNS}$ yet, but
a recent analysis based on the neutrino oscillation data prefers the phase
close to $270^\circ$.
