Why does the Long Run Philipps Curve say there is No Trade Off Between Inflation and Unemployment -What is said about the Significance of the Philipps Curve?

-Monetarists says that the Long Term Effect on Unemployment was Non-Existent. It always returns to the NRU -Therefore, they argued there was No Long-Term Link between Inflation and Unemployment -Some Economists argued the Short Run Philipps Curve doesn't even exist at all - the Trade-Off doesn't Exist! -Supply Side Policies can Lower Unemployment and Lower Inflation, which again, goes Completely Against the Philipps Curve. Sometimes though there can be a Trade-Off Existing, so the Philipps Curve is seen in usually Short Run Economic Policy Making