How many phases the Moon has depends entirely on who you ask. Western practice says eight, older European usage says four, and Indian and Māori calendars name every single night.

Four is what the naked eye reliably distinguishes — new, half, full, half. Eight is a modern convenience. Thirty tithis or thirty named nights is a different project altogether: not describing the shape but numbering the days. The Moon does not have phases; we have divisions, and we pick how many we need.