be on first name terms (with somebody)

To be on first name’s terms: se tutoyer

British English ( = be on a first name basis in American English) to know someone well enough to call them by their first name. “Graham and us have had a great business relationship for 5 years and Mitch is on first name terms with the CEO” // “(…) and she’s got herself on first-name terms with all the great and good (*) of the industry” // “He is on first-name terms with two former EU commissioners”.

(*) the great and the good are people who are considered important – used humorously.