When it comes to putting things in order, saying that something is at the "top of the list" is a common turn of phrase. However, there are several other expressions that can convey the same idea. For example, you might say that something is the "number one priority," the "biggest concern," or the "most pressing issue." Other possible synonyms for "top of the list" include "highest ranking," "most urgent," and "leading the pack." Whatever term you choose, the goal is to convey that this item or issue is the most important one, and should be given the most attention and consideration.