  The production of $\phi$ mesons in the reaction $e^{+}p \rightarrow e^{+}
\phi p$ ($\phi \rightarrow K^{+}K^{-}$) at a median $Q^{2}$ of $10^{-4} \
\rm{GeV^2}$ has been studied with the ZEUS detector at HERA. The differential
$\phi$ photoproduction cross section $d\sigma/dt$ has an exponential shape and
has been determined in the kinematic range $0.1<|t|<0.5 \ \rm{GeV^2}$ and $60 <
W < 80 \ \rm{GeV}$. An integrated cross section of $\sigma_{\gamma p
\rightarrow \phi p} = 0.96 \pm 0.19^{+0.21}_{-0.18}$ $\rm{\mu b}$ has been
obtained by extrapolating to {\it t} = 0. When compared to lower energy data,
the results show a weak energy dependence of both $\sigma_{\gamma p \rightarrow
\phi p}$ and the slope of the $t$ distribution. The $\phi$ decay angular
distributions are consistent with $s$-channel helicity conservation. From lower
energies to HERA energies, the features of $\phi$ photoproduction are
compatible with those of a soft diffractive process.
