Don't get so serious on the phone. Important issues are better discussed personally when a guy sees you and your relationship to your own words. On the phone you can arrange a meeting and to announce the theme for an important conversation or hint that such a conversation will be.
Be brave and confident. Even talking on the phone the young person can understand your mood: confusion, nervousness, fatigue. Keep calm and hidden. I can imagine that not talking to a young man that you like, and with an old friend or even a friend.
Do not quarrel on the phone and not find out relations with the guy. If a conflict has occurred, and you are still experiencing excitement and indignation, do not take the tube. Anything worthwhile you want. But if he's just brewing, invite the guy to meet and talk.
Stay friendly and polite. Be sincere, try to anticipate the desire of the young person, keep your dignity.