fall away vs phase down

fall away

verb
  • To diminish in size, weight, or intensity. 

  • To cease to support a person or cause. 

  • To get worse. 

  • To perish; to vanish; to be lost. 

phase down

verb
  • To gradually reduce the size or scale of 

How often have the words fall away and phase down occurred in a corpus of books? (source: Google Ngram Viewer )