称呼 (chēnghu) as a verb means 'to address someone as'—the full, polite way to say what you call someone, especially with a title. As a noun it's the form of address itself. Contrast with 称 (chēng, HSK5), a shorter, more literary verb used in fixed compounds (自称), and with 称号 (chēnghào, HSK6), which is an honorary or official title, not a daily address.