"In lock-step with" is a commonly used phrase that means to be synchronized or in perfect harmony with someone or something. There are several synonyms that can be used instead of this phrase. Terms like "in tandem with," "in sync with," "in agreement with," "congruent with," and "parallel to" can all be substituted for the phrase. Each of these synonyms conveys the same sense of being aligned or working in unison with something else. Using these synonyms can make your writing sound more varied and precise, and help prevent repetition and monotony in your language.