I'm with you on Coulomb's law but I don't see how you're relating it to voltage.

A voltage difference can be defined as the work done to move a charged particle between two points. Work is force times distance. If you move the points further apart the work to move the particle stays the same - the average force is lower but the distance is higher.

For example you can imagine a negatively charged Earth and a positively charged spaceship, and imagine moving an electron from the Earth to the ship. Near the Earth the main force on the electron is repulsion from the Earth. Near the ship the main force is attraction to the ship. In between it's a combination of both, but the force is relatively low. You need to integrate along the path to calculate the total work. So you can roughly break this down into 3 sections - near the Earth, near the ship, and the middle section. If the objects move further away, this stretches out the middle section, making the force lower but the distance longer. The main contribution at each end stays about the same. This is hand-wavey but I think it helps give an intuitive sense that the integral will work out the same as distance changes.

You can also consider the case of two objects with the same charge (equally positive or negative). The voltage difference between them is obviously zero, regardless of distance. But from Coulomb's law you know there is a force between them (repulsive) that depends on distance.