If one assumes that bugs are introduced at construction (the writing of the software) then you can use that as a fixed point to determine the cost of bugs based on when they are found. Which, using the original study, would mean that in testing the bugs would be more costly and that in production the bugs would be even more costly.
What is interesting is that it is a function of time and not phase. So, for example, if you were continuously deploying code and a QA found a bug the same day it would effectively be the same cost (assuming everything else is equal) as a code review done by a developer. It would also be significantly less than a bug found several months down the pipeline once your code was finally integrated into a QA environment in a non CD example.