Well, you can learn some strategic management by yourself. But something that would really be considered PhD level? That's a huge challenge. Like, I have a bachelor's, an MBA, a Master's, and even with the support of my advisor and faculty in general it is extremely hard. The PhD is a very different kind of beast.
So, I really suggest you to go slower. Books and courses are much more important for undergrad and master's, not PhD, but it's better to go that way first. Leave the PhD-level stuff for later.
As you get more knowledge and experience, then probably some topics will start to grab your attention, potentially becoming your topic of research in the future. Don't worry too much about it now. If you start reading papers from top journals, it will really depend more on which papers you can understand something, not on what would be a good topic for you.
Research is about things we still don't know. But first you need to learn what we already know (and that's already a major task). We build on existing knowledge.
Different people in different fields have different ways to find topics to write about. Sometimes, the topic comes from knowing the existing literature, and seeing the gaps. Sometimes, the topic comes from the type of datasets that you have available. Sometimes, the topics comes from challenges faced by firms.
In my case, the topic was a natural consequence of my professional career in industry. The problems the firms were not able to really solve in a good way, from my experience, became the topics of interest for my research.