How can I help to participate in data collection or research work as a field researcher? To clarify my question, due to length limitations in question part.

For PHD, Researcher allowed to take part as research subject for data collection/analysis? How to include personal accounts of/experiences of a research phenomenon? Thoughts/decision making processes when playing a specific game on world class level?

This then mean a specific game where there are limited /very few really have mastered the game and subjects are not easily contactable. Also potential research participants are a handful 5 to 12.

To explain. If a researcher want to ask how tennis players think his accessibility to the top 20 of the world tennis players are really only 20 and not just anyone around the corner that wannabee play tennis.
The first step before starting a PhD would be to find a potential supervisor who has some expertise in the research domain (not necessarily the specific topic). First there will be some discussion with this supervisor about the exact research topic and the motivations for the research: a PhD student's expertise in a particular topic is not enough to justify research on this topic, there must be some scientific reasons why this topic is a relevant research area.

Then you will see with your supervisor about the best method(s) to achieve these research goals. Imho it's unlikely that a supervisor would agree with a method which involves you as a subject, but I'm not at all in this kind of domain. In any case your expertise would certainly be useful in contacting subjects and targeting the right research questions.