have (got) (one's) number

To understand or know someone or something well enough to anticipate what they will do. That team is impossible to beat—they've had our number since 2006! Oh, don't worry, I've got his number—he's a typical brat. She caught me by surprise last time, but I've got her number now, and I won't let her manipulate us again.

have someone's number

If you have someone's number, you understand what kind of person they are, and so you know how to deal with them. Oh, don't worry — I won't let him cheat me. I've got his number.

have someone's number

understand a person's real motives or character and thereby gain some advantage. informal