Where to disable pop ups for a particular website on iPhone?

For Safari, yes. There is no website specific control, as most pops are not actual system based notifications but custom popups on the website, which only they control.

So either you block them all, or you live with the ones you don't want.

Other browsers, may have other options.

That would depend on the browser you are using. For Safari, you can turn off Popups in Settings ➡️ Safari.

For other browsers check their settings. Or turn them off completely in Settings ➡️ Notifications ➡️ Browser Name