This Fourth of July puzzle has two numbers in each of ten different states. The key realization here is that each state can also be represented by a two-letter abbreviation. The numbers each can be paired up with a letter in this way. For example, Oregon (OR) has the numbers 20 and 11, so 20 = O, and 11 = R.
Noticing that there is exactly one of each number from 1-21 excluding 19, solvers can put the letters in numerical order to get CRACKEDAMERICANSYM?OL. The missing letter is clearly a B (which doesn’t appear in any state abbreviations, though it appears in the abbreviations for four different Canadian provinces), giving the clue phrase CRACKED AMERICAN SYMBOL. This is a reference to the LIBERTY BELL.
*Apologies to anybody who tried removing the B and submitting LIBERTY ELL as the answer. While that would be clever, it doesn’t make sense as a phrase.