What a phenomena should look like
The phenomena you chose, or the lens through which you want to present your content, should be something that allows you to start with something small and then be able to build on the same idea or concept, or explore the same idea in more and more detail.
Phenomena should be a question that is universally seen or understood by your students. This typically means asking a question that is directly related to their lives, something they have seen before or experienced before. This connection increases student engagement in the classroom, but more than that the students will apply this knowledge or engage with other people outside of the classroom because again the student experiences it regularly in their lives. A good phenomenon is a question that takes experiences that is easily observable and relatable and makes the students question this observation in a new way. Some teachers allow their students to develop their questions, but I find students aren’t sure what questions to ask without support. This can cause students to miss the point or feel self-conscious about not asking the right question. I find it easiest to have cohesion and guide the students to what I am intending for them to learn if I allow the students to generate a large list of questions and then choose the ones that are related to the intended topic. Then I let the students choose from the list any question because they are all directly related to one or more of our standards.
If you would like your students to develop their questions, then the best way to do this is to have students brainstorm. Have students make questions, and let them write down as many questions as they can think, just make sure to have a minimum number of questions and students have a clear idea of what topics and kinds of questions they should be asking. Students should do this individually. Then have students share these ideas, so students without questions can develop ideas and students with questions can potentially think of new ones. Collect all of the questions and compile them into a single list. Then let students choose among the questions, which would they like to learn more about.
Phenomena should not be something students can google the answer to, but this is not realistic in all aspects. Your phenomena can be specific to a student's project/activity, like a project about how tall will beans grow when given 6 hours of light vs 8, is not easy to google, otherwise, google can answer most questions students ask. However, google can answer many questions; the real trick is to weed out phenomena/questions that have no depth. They are simple answered questions, like what color is the sky, this is not a viable phenomenon, but why is the sky blue, is a great phenomenon. Students can google the answer, but it doesn't mean they truly understand the answer, and as the teacher, you can guide the learning to go into more and more depth than blue light scattering as an answer. Students can develop many kinds of experiments for this type of question.
You should have only one phenomenon per unit. Some teachers try to do new phenomena every day. This is not only very difficult and stressful, but it is also difficult for students to understand how each is connected. Having only one phenomenon allows for in-depth knowledge of that topic and allows for broader connections and implications.