  We study exclusive $\pi^+ \pi^-$ pair production near $\rho^0$ resonance peak
in ultraperipheral heavy ion collisions. Pion pair can either be produced via
two photon fusion process or from the decay of $\rho^0$ in photon-nuclear
reaction. At very low pair transverse momentum, the electromagnetic and nuclear
amplitudes become comparable. We show that the Coulomb nuclear interference
amplitude gives rise to sizable $\cos \phi$ and $\cos 3\phi$ azimuthal
asymmetries, which can be used to constrain the phase of the dipole-nucleus
scattering amplitude.
