If I am citing a book for reference in a PhD thesis, but cannot get
hold of the actual work, will this be accepted? also when searching to
confirm the details of publication for a title with 2 publishing
countries, is it preferred to give both countries or is this
nonessential?

The real answer to your question depends on the specific instructions
you receive from your university. These are typically guidelines which
are provided by your university library since they are ultimately the
custodians of the finished document.

However, with that disclaimer, I can still provide a probable answer
to your questions.

There should be no problem citing a book you cannot get into your
hands as long as you have reliable information about it (such as a
library catalogue entry). Of course, your thesis committee may wonder
why you want to cite a work you are clearly not using directly in your
research. I'm presuming you have a good reason to want to cite the
work, or perhaps you have a secondary source for some of its content.

As to the details of publication, _The Chicago Manual of Style,
Fourteenth Edition_ (Chicago[and London!]: The University of Chicago
Press, 1993), 555-56 recommends (in paragraph 15.157):

"The name of the city where the publisher's main editorial offices are
located is usually sufficient:

   New York: MacMillan, 1980

"If the title page of the book lists two cities with the publisher's
name, the city listed first is the one to use; it is permissible, but
not necessary, to use both:

  Chicago: The University of Chicago Press, 1991.
  Chicago and London: The University of Chicago Press, 1991."

The Chicago Manual is widely used by English-language journals as a
style reference, but it is by no means the only such reference
available, and specific details do vary from one style manual to
another. I hope that answers your question!

This reply from drdavid is very good. I'd suggest some useful links
ought to be included.
The response from Catherine points to a very useful link, but there's
no 'added value' (so only 2 stars there, I think).
Happy to pay my $4!

Referencing styles vary depending on the discipline. Links to
guidelines by subject are given here:

Resources for Documenting Sources, from Purdue University Online
Writing Lab.
http://owl.english.purdue.edu/handouts/research/r_docsources.html.

This is a good link, but there's no added value - e.g. a few examples,
especially one showing how the second part of my question might be
addressed.

BTW, it is not a "PhD thesis". It is a Ph.D. dissertation.