Answer:
Rehearsal
Step-by-step explanation:
Rehearsal is an strategy used when it comes to memory, this strategy consists in repeating the information you need to remember in order to get it processed and stored. In other words, it is about repeating information without thinking about its meaning or connecting it to other information.
Usually, once you stop repeating the information, it disappears from your mind and you cannot recall it anymore.
In this example, you keep repeating your friend's number over and over so that you will be able to enter the number in your cell phone once you get to it. You are repeating the information you need without thinking about its meaning or connecting it to other numbers. Once you store the number on your phone, you'll forget the number you've been repeating. Thus, this is an example of the memory strategy of rehearsal.