back off vs phase down

back off

verb
  • To lower the setting of. 

  • To become less aggressive, particularly when one had appeared committed to act. 

  • To move backwards away from something. 

  • You need to back off, or the situation could turn ugly. 

  • Used other than figuratively or idiomatically: see back, off. 

phase down

verb
  • To gradually reduce the size or scale of 

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