Ph.D Research - Can you make yourself irreplaceable?

A while ago, I had dinner with this lovely young eastern European woman. It was our first encounter. She has been living in the UK for only two weeks. she had already a job and an accommodation. We started talking about our academic achievement. She mentioned that she had a master in digital literature. I suggested that she could possibly do her Ph.D at the University of Reading. She shrugged and said

 'I have been working as a research administrator in a university for two years. I was the one who convinced students not to do their Ph.D. 

Ph.D students slave themselves away for three years of their life. They carry out valuable research, write papers and go to conference, yet they are underpaid and they will probably not get a job at the end of it. Academia is an industry where Ph.D are a herd being truthfully exploited.'

It was partially true.

I started my Ph.D to escape the dogma of some other mainstream form of exploitation

I wanted to be my own project.

Academia appeared to be a door to freedom.

Yet, my value and future truly depend on research area, trends and interests. The week following to that I found myself thinking more than once that I could possibly leave my Ph.D.

Be self-employed and do whatever I want.

I did not.

Employed or self-employed, it remains the same. Your future actions are dictated by who needs you and how easy you can be replaced.

I am wondering how one can make themselves irreplaceable?