  We obtain a phenomenologically acceptable PMNS matrix in a flipped SU(5)
model inspired by the compactification of heterotic string $E_8\times E_8'$. To
analyze the Jarlskog determinant efficiently, we include the simple Kim-Seo
form for the Pontecorbo-Maki-Nakagawa-Sakata matrix. We also noted that
$|\delta_{\rm PMNS}|\lesssim 64^{\rm o}$ for the normal hierarchy of neutrino
masses with the PDG book parametrization.
