The standard thesis structure has four parts: an introduction, the background, the core, and a synthesis.
The introduction explains what the thesis is about: the problem that the thesis is concerned with, the aims and scope, and the thesis structure.
The background is the knowledge required before a reader can understand your research: relevant history, context, current knowledge, theory and practice, and other researchers’ views. In the background, your purpose is to position your study in the context of what has gone before, what is currently taking place, and how research in the area is conducted. It might contain a historical review.
The core concerns your own work: your propositions or hypotheses, innovations, experimental designs, surveys and reviews, results, analysis, and so on.
The synthesis draws together your contribution to the topic. It will usually contain a discussion, in which you critically examine your own results in the light of the previous state of the subject as outlined in the background, and make judgments as to what has been learnt in your work; the discussion may be a separate chapter, or may be integrated with the detailed work in the core.
Finally, it is where you summarize the discussion and evaluation to produce conclusions. These should respond directly to the aim of the work as stated in the introduction. The structure of the core varies greatly from discipline.
Just as there is no uniform standard for the structure of a PhD thesis-book, so too there is no standard way to structure a synopsis of one. This is because the PhD thesis-book has to be novel, and that novel content dictates its form. If you want to summarise a PhD thesis-book, you would do well to copy its Abstract, where the author has done his/her best job to give an overall view of the thesis-book.
I think the question was about the *Synopsis*, not for the Thesis itself. Different institutions have their own suggestions. Here a couple for the Synopsis: