How do I tell him I like him?

*Note: I am a sophomore in highschool.
I'm interested in someone. And I see him every day. We talk like casual friends and he confides in me sometimes. He sits next to me in World Geography so that's where I tend to see him most. I have his number but he lost his phone so that gives me no realistic way to speak to him outside of school.
In thinking about how to let him know that I like him and want to hang out, I've encountered a few issues.
1) His really close (And Vexatious, might I add) friend sits right behind me so I wouldn't be able to verbalize any hanging out unless his friend wasn't there at the risk of his friend bothering me and telling others.
2) If I write it in a note and he somehow manages to keep it, he will have it in writing. He could show his other friends and humiliate me. Not saying that I lack trust in him, but I've been through that before.
3) Approaching him outside of class would be extremely risky, given that he hangs out with all his other friends that I fear. I don't want to be humiliated.

That brings me to what I need to know.

How should I approach him, with what method and what wording should I use when I do decide to approach him?
How do I tell him I like him?
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