If you look at the bottom of the link you posted, there is a link to pub 972 which has a worksheet. Basically, you take 110k off whatever your AGI is, so let’s say your AGI is $130k. You take the difference (in this case 20k) and multiply it by 5%, which would be $1,000. You subtract that total from your total tax credit. So w/ 1 kid it’s fully phased out at 130k, 2 kids @ 150k, 3 kids @ 170k and so on. Or for any number inbetween there, you basically lose $50 of the credit for every 1,000 in income (5%).