The PhD hits the workforce ~6 years later than the undergrad. It is entirely feasible, in fact most probable, for a 80k undergrad to hit ~115k in 6 years.
However, salary usually climbs fastest in the first few years after starting, so if they are both at 115K at some point, the next year the PhD may be at 126, while the undergrad get stuck at 118. This difference only increases and the end-of-career opportunities for the PhD are also larger: on average, he can attain jobs for which he will be preferred above the undergrad, who gets stuck at a lower rung. Of course, this is all 'on average'.
