  Motivated by the experimental measurement of the decay rate, $\Gamma$, and
the longitudinal polarization, $P_L$, in the Cabibbo favored decay $D_s^+\to
\phi {\rho}^{+}$, we have studied theoretical prediction within the context of
factorization approximation invoking several form factors models. We were able
to obtain agreement with experiment for both $\Gamma$ and $P_L$ by using
experimentally measured values of the form factors $A_1^{D_s\phi}(0)$,
$A_2^{D_s\phi}(0)$ and $V^{D_s\phi}(0)$ in the semi-leptonic decay $D_s^+\to
\phi l^{+}\nu_{l}$. We have also included in our calculation the effect of the
final state interaction ($fsi$) by working with the partial waves amplitudes
$S$, $P$ and $D$. Numerical calculation shows that the decay amplitude is
dominated by $S$ wave, and that the polarization is sensitive to the
interference between $S$ and $D$ waves. The range of the phase difference
$\delta_{SD} = \delta_S - \delta_D$ accommodated by experimental error in $P_L$
is large.
