Like any other writing project, brainstorm for ideas. Explain the feelings related to the event. Whatever your subject, think about ways to describe what is felt in the moment in a tone that is enticing, and make sure to write in detail about the experience.
The key to narrative essay writing is to be descriptive. Remember that the writer serves as the reader's senses. It is important to visualize the scenario as if the reader is the one experiencing the scene. Every aspect of the experience, every detail that happened in the moment, find a way to put those into colorful words. Before beginning, think of the highlights of the event. Ask questions about it.
Was the phone a surprise gift? Did you know it was coming, but you had to wait for it? Were other people involved?
Start with what happened before you got the phone. For example, if the phone is a birthday gift but was contingent upon good grades, write about that. Explain some of the work you had to do. Tell the reader about your anticipation. Perhaps start your essay on the day the school issues report cards.
It does not matter if the topic is intense, light, routine or extraordinary. What matters is how you put the experience into words.