It depends on where you are applying to. Usually all grants and institutions have their own guidelines, you should check them first. Second, contact your future supervisor.
Indeed, all the universities that offer doctoral programs have prioritized lines of research and protocols that detail the preparation and presentation of the thesis as well as the defense of it.
Hi, bro, as per my expereince, i will suggest you to contact with your supervisor first, for sure he/she will give you some outlines & then according to that university requirments you can write an research proposal. First, find Professor related to your research theme , mail him & tell him that you want to do PhD under his supervision, if he agreed then for sure he will sent you a letter in which he will mention the topic of your research, then you can write an your research proposal.
I hope this will help you. If any other other help is needed, feel free to ask.