Based on the phase-space information obtained from a multi-phase transport model within the string melting scenario for strange and antistrange quarks, we study the yields and transverse momentum spectra of $\phi $ mesons and $\Omega $ ($\Omega ^{-}+\bar{\Omega}^{+}$) baryons as well as their anisotropic flows in Au+Au collisions at RHIC using a dynamical quark coalescence model that includes the effect due to quark phase-space distributions inside hadrons. With current quark masses and fixing the $\phi $ and $\Omega $ radii from fitting measured yields, we first study the ratio of the yield of $\Omega $ baryons to that of $\phi $ mesons as well as their elliptic and fourth-order flows as functions of their transverse momentum. How the elliptic and fourth-order flows of $\phi $ mesons and $\Omega $ baryons are related to those of strange and antistrange quarks is then examined. The dependence of above results on $\phi $ and $\Omega $ radii as well as on the strange quark mass is also studied.