How and when should I ask him for his phone number?

I'm 13 and in sixth grade but still in elementary school and so is the guy I like. I'm determined to ask him for his number this week but idk when during the day or what exactly to say. We both have the same home room in the morning first then 1st period. I have social studies and so does he. We then go back to home room and then go to special. When we get back to home room we go to second period science and we both have that together. We then go back to home room and go to lunch. We come back and then go to third period math which we have together and then we go strait to I/E or star time but we don't have that together. We go back to home room for the rest of the day. He's almost always tlking to someone so idk how/when to ask him or what to say???