  The $\phi$-$\Lambda(1520)$ interference effect in the $\gamma p\to K^+K^-p$
reaction has been measured for the first time in the energy range from 1.673 to
2.173 GeV. The relative phases between $\phi$ and $\Lambda(1520)$ production
amplitudes were obtained in the kinematic region where the two resonances
overlap. The measurement results support strong constructive interference when
$K^+K^-$ pairs are observed at forward angles, but destructive interference for
proton emission at forward angles. Furthermore, the observed interference
effect does not account for the $\sqrt{s}=2.1$ GeV bump structure in forward
differential cross sections for $\phi$ photoproduction. This fact suggests
possible exotic structures such as a hidden-strangeness pentaquark state, a new
Pomeron exchange and rescattering processes via other hyperon states.
