The accelerometer will read 9.8m/s^2 along the axis of the centrifuge, because that is the acceleration that is keeping the phone moving in a circle instead of

The accelerometer will read 9.8m/s^2 along the axis of the centrifuge, because that is the acceleration that is keeping the phone moving in a circle instead of flying into space. The difference between that and resting the phone on the Earth is that the centrifuge structure is accelerating it by exerting force on it, whereas the Earth is accelerating it by altering the spacetime metric in its vicinity. Completely different mechanisms, same reading.