Its just showing you the dillutions.

You start out by making a master mix of 1000ppm.

From there you are dilluting down to 100, 10, 5, 4, 3, 2, 1 ppm solutions from the 1000ppm 1l solution with RO/DI water.

If you really are intent on testing PO4 you can use the 1000ppm solution to make stock reference solutions. Get some empty bottles and store stock solutions (5,4, 3, 2,1 ppm ). From that chart even making 1/2 solutions (4.5, 3.5, 2.5, 1.5, .5) to be even more accurate. So before you test your tank water have plenty of vials ready. Then test your tank water and stock solutions at the same time. Then you can match to the closest solution. The point being that you are not using a color chart but a closest match to known solutions.

So to be partially acurate at 1/2 ppm intervals from .5 - 5 you will be making 10 seperate solutions plus the tank water so a total one time test of 11 vials.

I can't see being accurate by making a solution of say 3ppm. Checking the color chart and going off of that. Most if not all of the hobbyist grade PO4 tests are
1) innaccurate
2) have poor color charts to determine PO4 levels
4) Have wide gaps in the chart once you are over 1ppm.
API - 0 - 0.25 - 0.5 - 1.0 - 2.0 - 5.0 - 10.0
Salifert - 0 - .03 - 0.1 - 0.25 - 0.5 - 1.0 - 3.0
5) Matching colors to these charts is problematic at best.

This is why I can only see making as many reference solutions as possible and testing all at the same time. Otherwise IMO you are going to be wasting your time.

Your readings can vary for alot of reasons. Some tests require shaking the bottle vigorously prior to use. What happens if you forget? What does that do to the solution the next time you use it? So if you only do a one time calibration and continually go off of that reading, IMO you are just fooling yourself. API's Nitrate test kit comes to mind. I found Silifert's PO4 to be the easiest but still very difficult to get consistant readings from known stock solutions due to the damn little spoon and large granual reagent.

What I"m trying to get at, and I'm not trying to dissuade you from testing if you truly feel the need to. Hobbyist test kits are very problematic and to test properly with them requires a great deal of effort to calibrate them to get an accurate reading. Hope this helps and good luck.