This. A PhD can ask for a higher salary than a master student, but a person with a master and 5 years of experience can ask for a higher salary than a PhD student.

I wonder if having a PhD will allow faster growth to a senior position such that a PhD will win out in the long term. I'm guessing on average the difference is not that big in the long term.

As others have said: ask yourself why you want to do a PhD. If it is to get a higher salary, you might want to think again.