Optically trapped polar molecules are promising for quantum information processing, yet the accuracy of an entangling molecular gate is limited by the uncertainty of dipole-dipole interactions~(DDI) from the molecular motion in traps. We show that two $\pi$ pulses of global microwave excitation can yield a spin-echo controlled-phase gate when assisted by two single-qubit gates, where the gate is resilient to the uncertainty of DDI because it strongly suppresses populating DDI-coupled states. Further, the controlled phase is fully tunable by varying the relative phase of the two global microwave pulses, and, hence, is applicable in a wide range of quantum algorithms involving quantum Fourier transform. We introduce a motional-mode separation technique to quantum mechanically study the influence of the molecular motion, which shows that the motion-induced infidelity of the gate can be below 0.0001 with typical experimental conditions.