Photoproduction of $phi$-meson on protons was studied by means of linearly polarized photons at forward angles in the low-energy region from threshold to $E_{gamma}$= 2.37 GeV. The differential cross sections at $t = -|t|_{min}$ do not increase smoothly as $E_{gamma}$ increases, but show a local maximum at around 2.0 GeV. The angular distributions demonstrate that $phi$-mesons are photo-produced predominantly by helicity-conserving processes, and the local maximum is not likely due to unnatural-parity processes.
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