Your question is somewhat unclear.
But generally speaking, if the preposition part of the phrasal verb is at the end of the sentence, it is stressed but in the middle of the sentence, it is unstresed.
You need to clean up. -- The stressed words are 'need,' 'clean' and 'up.' The words 'clean' and 'up' get the same stress.
You need to clean up the mess. The stressed words are 'need', 'clean' and 'mess."