To reinforce tadrinth's comment: even if a PhD were to offer to work for a BS salary, employers would have to ask why. Is it because the PhD knows their work quality is that far below their peers? Is it because they just want a job to "tide them over" while they search for a better paying offer elsewhere?

On an unrelated note:

When planning for the future you need to consider stupid central planners as carefully as smart computers/robots. PhD employment rates have seemed happily immune to the present economic troubles, but the next round of trouble is going to come when government budgets revert toward equilibrium, and that process may be particularly hard on jobs which closely depend on government funding.