In a PhD dissertation, can one copy the structure of the acknowledgment section from their own or from someone else's prior work?
First, throw away everyone else's acknowledgements sections. Ignore them.

Second, think of all the people to whom you feel grateful, and write down your thanks in whatever way feels natural to you.

It really is that easy. There's only so many ways to say something, so if it sounds similar to someone else's, so what? As long as they are your own heartfelt words, no one will notice or care.