I have not personally heard of an enlarged prostate causing interference with bowel movements - but.....
the location of the prostate does make it a candidate in interfering with the rectum. Please go look at the diagram at this link:
See where the prostate is in relation to the rectum? If the prostae became really, really enlarged, in theory it could put pressure on the rectum. That pressure in theory could make it difficult to have a BM. Can I ask why you are asking? In this a problem you are having? Or are you questioning a diagnosis you were given? No need to answer if none of my business...I'm just curious.