Why would a poet vary the number of feet in lines of poetry?

When the telephone rings incessantly, what is it that the men want to have happen? they want the phone to be answered because it is jangling their nerves. they want mr. frank to go to the office and answer it because they are afraid it might be bad news. they want mr. frank to go to the office because they think it might be miep. they want mr frank to ignore the phone.