A reversible gradual L2(1)-to-10M/14M phase transformation at low stress is shown via in-situ nanoindentation on a single crystalline Ni54Fe19Ga27 alloy. At higher stress, an irreversible abrupt transition from residual L2(1) to L1(0) martensite (a 2nd type of phase transformation) occurrs. This study provides new perspectives for understanding stress induced phase transformations in magnetic shape memory alloys.