Even though each word we read or speak has its own meaning, we generally don't read, speak or think of each word by itself. We tend to group words together into phrases. We can have entire conversations in phrases, and if we want to be sure we're understood, we often pause to emphasize the most important phrases.
Understanding phrases while reading can help fluency and comprehension. When trying to read something complicated that doesn't seem to make sense, it's very helpful to go back and read it one phrase at a time to figure out just where understanding stopped. If you want to savor a book, or are having trouble paying attention to something you're reading, you can read one phrase at a time, imagining how it would sound, and you can make a mental picture of it or re-phrase it in your own words.
You can make reading in phrases easier by lightly underlining (usually with a slight scoop, as if drawing a spoon to hold the phrase) phrases as you read. Re-reading a passage emphasizing the phrases can make it easier to read smoothly and with feeling. Repeated reading has long been known to help fluency and comprehension.
Source : Susan Jones, M.ed