This paper reports the successful attenuation of self-exciting thermoacoustic instabilities inside a gas turbine matrix burner using phase-shift control. The test rig configuration is a matrix burner suitable for simulating the conditions prevailing in stationary gas turbines. The geometry consists of three main parts: 1. a mixing chamber where gaseous fuel is injected into the incoming air stream, 2. a contraction into several small slots which prevents upstream flame propagation, and 3. the combustion chamber. The fuel is first injected upstream before a high incoming velocity air forces it to move downstream. This design enhances fuel/air mixing by increasing the residence time of the mixture in the mixing chamber. But, introducing this time lag will lead to combustion instability in the matrix burner if it is approximately in phase with an integer multiple of the acoustic period. Phase shifting was done using a loudspeaker in one case and a fast response injector in another case to modulate the inlet air and primary fuel streams respectively. The dominant modes in each case were successfully suppressed with that due to the loudspeaker achieving a 45% reduction and the pulsed primary fuel injection achieving a 70% reduction. In both cases, however, secondary peaks were generated due to a coupling of the controller and the dynamics of the test rig. PIV measurements of the cold flow velocity field are first reported and compared with CFD results. This is followed by the determination and the explanation of the stability map of the matrix burner from measurements. Finally the pressure monitored inside the combustor of the matrix burner using unsteady CFD is validated with that obtained from microphone measurements.