How to configure PBS buffer with PH 3 and 8?

PBS is phosphate buffer, and its effective PH is about 7.4. PBS with PH 3 is meaningless, and it can't be matched with hydrochloric acid or barely adjusted to this PH, and it has no buffering power, while PBS with PH 8.0 can be matched. To put it simply, add 8g of sodium chloride to 1L, then weigh 0.0 1M sodium dihydrogen phosphate, dissolve it in about 600ml of water, and adjust the PH value to 8.0 with sodium hydroxide. If you have experience, you can also add a certain proportion of sodium dihydrogen phosphate and disodium hydrogen phosphate to control the PH value at 8.0.