Phone is a sort of short hand for what tradeoffs are likely in the chip. A phone processor is going to prioritize efficiency and thermals over raw performance. Mobile will strike a different balance. While desktop likely prioritizes raw power over performance per watt, thermals be damned!

Of course, that same "phone" processor gets to operate with battery and thermal headroom of a laptop in the Macbook Neo. The bigger trade-offs are due to the device the chip operates within.