Adverb
on a first-name basis (not comparable)
(idiomatic) Having enough familiarity with another person to call them by their first name, as opposed to their surname.
We are not yet on a first-name basis.
Eddie, who was on a first-name basis with all of Texas, was a self-made man, having started an oil supply company with two trucks and a few employees. Source: Internet
Over the last 13 years, she said she's come to know many customers on a first-name basis and is accustomed to running into them at local grocery stores. Source: Internet
Yet the chamber created its biggest fury in Montana, a small-population state where politics operate on a first-name basis. Source: Internet