  As part of a measurement of the cross section of $\phi$ meson photoproduction
to high momentum transfer, we measured the polar angular decay distribution of
the outgoing $K^+$ in the channel $\phi \to K^+K^-$ in the $\phi$
center-of-mass frame (the helicity frame). We find that s-channel helicity
conservation (SCHC) holds in the kinematical range where $t$-channel exchange
dominates (up to $-t \sim 2.5$ GeV$^2$ for $E_{\gamma}$=3.6 GeV). Above this
momentum, $u$-channel production of a $\phi$ meson dominates and induces a
violation of SCHC. The deduced value of the $\phi NN$ coupling constant lies in
the upper range of previously reported values.
