"Up" is an adverb with qualifies the verb "pick". As we saw last week, if the particle is a preposition, the substantive (noun) has to go after it. It isn't the same with adverbial particles. Consider these two examples:
- We have to call the client back [or "We have to call back the client"].
- He needs to clean his room up [or "He needs to clean up his room"].
As long as the phrasal verb is transitive, we can place the noun before or after the adverbial particle. Here's another example of a "[verb] + [adverb] = adverbial [phrasal verb]" formula:
- Pay [verb] + back [adverb]. "I'll pay the money back soon." Also "I'll pay back the money soon."
Because the particle, back, is an adverb, the noun can follow it or precede it. In other words, we can say "I asked you to put your bag down or I asked you to put down your bag. There is no difference.