The phrase "crowd in on" implies a sense of compression or suffocation, a feeling of being surrounded or overwhelmed by a mass of people or objects. While this expression perfectly captures this sensation, there are other synonyms that can be used interchangeably to diversify your writing. One such synonym is "close in on," which conveys the same sense of being hemmed in on all sides. "Encroach upon" is another term that can be used to describe when something or someone is infringing upon your personal space, while "press upon" suggests a closer physical proximity where the people or objects are right up against you, causing discomfort or hindrance in movement.