Historically, when the Phillips curve was steeper, inflation tended to rise as the economy heated up. The rise in inflation would prompt the Federal Reserve to raise interest rates to restrictive levels, which would have the effect of tightening financial conditions more broadly.
In contrast, the past few cycles did not see this kind of behavior, and in each case, financial imbalances, rather than goods and services inflation, were notably elevated at the onset of the downturn.