Answer:
The effect that the repetition of the phrase "when I watch you have on the poem is that It gives the poem a sense of rhythm.
Step-by-step explanation:
The question is not complete since it does not provide the poem of reference, here is the poem:
Read "Miss Rosie" by Lucille Clifton.
when I watch you wrapped up like garbage sitting, surrounded by the smell of too old potato peels or when I watch you in your old man's shoes with the little toe cut out sitting, waiting for your mind like next week's grocery I say when I watch you you wet brown bag of a woman who used to be the best looking gal in Georgia used to be called the Georgia Rose I stand up through your destruction I stand up read "miss Rosie" by Lucille Clifton.
One of the main reasons why writers use repetition in their poems is because it helps to define the rhythm of it, even when there are other functions of repetition in poetry such as giving importance to some part in specific or setting the tone, the rhythm keeps being the key point in the repetition of this poem.