taper off
phrasal verb with taper verb [ I or T ] uk/ˈteɪ.pər/ us/ˈteɪ.pɚ/
逐渐变小;逐步减弱
to become gradually smaller or weaker, or happen less often
Her voice tapered off as she realized everyone was listening. 当她意识到大家都在听时，她的声音就越来越小了。
Sales have gradually tapered off. 销售额逐渐下滑。