First-name basis

If you’re on a “first-name basis” with someone, your relationship is close enough that you address each other using first names. “First-name basis” implies a level of familiarity. Larry King was on a “first-name basis” with the most famous celebrities, the most powerful politicians, and millions of callers and viewers. Larry King was familiar with many powerful people. All of the dinner party guests were on a “first-name basis.” The manager is on a “first-name basis” with the CEO of the company.