A PhD proposal refers to an outline of the planned project that aims at stating a question clearly along with a systematic approach to answer it, emphasizing its originality and importance, and explaining its contribution to the development of the current literature. A research proposal usually tends to differ in length, scope, and structure due to which you need to work as per the guidelines fixed by the institution.
A research proposal is also a source of assessing as well as delegating suitable supervision teams. In case you are fascinated about the work of a specific supervisor or have discussed about your topic with her or him, it is wise to mention this in the PhD proposal. However, it is firmly advised to identify a potential supervisor and discuss about the proposal informally prior to a formal application. Doing so ensures that both are mutually interested in the research as well as in obtaining information about the design and scope of your project. Nevertheless, getting a specific academic supervisor might not be guaranteed.
A good PhD proposal tends to emerge as you progress. It is usual for the authors to hone their original proposal in terms of exhaustive literature reviews and supplementary consideration of approaches and feedback obtained from the supervisors as well as other academic staff members.