The phrase "sound a knell" is often used to describe an ominous or foreboding feeling, especially when referring to the end of something or the beginning of a new era. There are many synonyms that can be used in place of this phrase, depending on the context. Some possible options include "ring the death knell," "herald the end," "usher in a new phase," "mark the passing of," and "announce the closure of." Each of these phrases conveys a sense of finality or change, and can be used effectively when discussing the end of a project, the retirement of a colleague, or any other major shift in circumstances.