The St Louis Fed writes (my emphasis):
During the 1960s, some economists made the case that the Phillips curve—a negative relationship between the inflation rate and the unemployment rate—represented a tradeoff for policymakers. So, according to this view, a central bank could achieve permanently lower unemployment by accepting higher inflation. However, beginning with Milton Friedman in 1968, other economists made the case that the Phillips curve tradeoff was not permanent. According to this alternative view, the Phillips curve correlation might be observed in the data over some periods of time, depending on the types of shocks hitting the economy, but a central bank could not exploit a Phillips curve tradeoff to create permanently low unemployment. Then, beginning in the 1990s, New Keynesian economists propelled a resurgence of interest in the Phillips curve, which plays a prominent role in New Keynesian theory.Murray Rothbard many years ago pointed out the problems with the Phillips Curve:
The graph shows the Phillips curve we observe in the data following the end of the Great Recession. The data run from June 2009 to August 2015, and the line connects the points in the scatter plot in temporal sequence running roughly from right to left in the graph. Over this period, the Phillips curve slopes the wrong way—a higher unemployment rate is associated with a higher inflation rate.
Originally, the Keynesians promised us that by manipulating and fine-tuning deficits and government spending, they could and would bring us permanent prosperity and full employment without inflation. Then, when inflation became chronic and ever-greater, they changed their tune to warn of the alleged tradeoff, so as to weaken any possible pressure upon the government to stop its inflationary creation of new money.
The tradeoff doctrine is based on the alleged "Phillips curve," a curve invented many years ago by the British economist A.W. Phillips. Phillips correlated wage rate increases with unemployment, and claimed that the two move inversely: the higher the increases in wage rates, the lower the unemployment. On its face, this is a peculiar doctrine, since it flies in the face of logical, commonsense theory. Theory tells us that the higher the wage rates, the greater the unemployment, and vice versa. If everyone went to their employer tomorrow and insisted on double or triple the wage rate, many of us would be promptly out of a job. Yet this bizarre finding was accepted as gospel by the Keynesian economic establishment.
By now, it should be clear that this statistical finding violates the facts as well as logical theory. For during the 1950s, inflation was only about one to two percent per year, and unemployment hovered around three or four percent, whereas later unemployment ranged between eight and 11%, and inflation between five and 13 %. In the last two or three decades, in short, both inflation and unemployment have increased sharply and severely. If anything, we have had a reverse Phillips curve. There has been anything but an inflation- unemployment tradeoff.BTW The Phillips curve is one of Fed Chair Janet Yellen's favorite indicators:)