Let's check the phone application "buffers" for it's ability to calculate how to prepare a phosphate buffer.

Suppose I want $1$ liter of a $0\mathrm{.}1M$ phosphate buffer at a pH of $6\mathrm{.}8.$

Phosphate has a pK$2$ of $7\mathrm{.}2$

MW of monosodium phosphate $Na{H}_{2}P{O}_4($aka monobasic$)$ is $119\mathrm{.}98$

MW of disodium phosphate $N{a}_{2}HP{O}_4($aka dibasic$)$ is $141\mathrm{.}96$

Let's first calculate the fraction of dibasic we need from the $H-H$ equation. In other words solve for

A$-/$total$.$

Calculate to $3$ sig figures