Oxides with Brownmillerite type structure have been reported to show low-temperature oxygen mobility down to ambient temperature, making them an attractive class of compounds in the field of solid-state electrolytes. We have recently studied the 1D moderate temperature mechanism of oxygen mobility in Brownmillerite phase of Sr2ScGaO5 and it is for us intriguing to now discover comparable moderate temperature conductibility for the more compact and isotropic oxygen deficient cubic phase. We aim to explore the impact of oxygen diffusion on lattice dynamics in this cubic oxygen-deficient Sr2ScGaO5 by following, with IN4 instrument, the modification of its gDOS in function of temperature around the onset of oxygen mobility. In this way we would be able to correlate the impact of structure and dynamics on its moderate-temperature oxygen ion diffusion mechanisms which should more likely follow a 3D diffusion scheme. This system represents a promising candidate to shine more light on the interplay in between structure, lattice dynamics, oxygen deficiency and site occupancy order in the onset of oxygen mobility at moderate temperature.