Here's why:
* Verb + Preposition: It's made up of a verb ("pick") and a preposition ("up").
* Combined meaning: The meaning of "pick up" is different from the separate meanings of "pick" and "up." For example, "pick up" can mean to lift something, to collect someone, or to learn something.
Here are some examples of "pick up" used as a phrasal verb:
* "Please pick up your toys." (meaning to lift and put away)
* "I'll pick you up at 7 pm." (meaning to collect someone)
* "He picked up Spanish quickly." (meaning to learn something)