Phrases are probably the most essential unit of language but so little is written about them.
One of my professors at UC Irvine wrote a books called The Differend, which placed the phrase not just at the center of writing but at the center of what is. Doing this always struck me as somewhat odd since words were smaller units and letters even smaller still. But he was not writing about the units we have broken our language down into as much as he was writing about the units of thought.
We just do not think word by word. We think in phrases and sometimes in clauses. This is where I think much of the discussion and instruction in grammar misses the mark. Without a doubt we run into problems at the level of individual words. We misspell words, not phrases and clauses. We look up words in the dictionary, not phrases and clauses. We search for just the right word, but rarely struggle with just the right phrase or clause. And we mock people who misuse words in the speech, not people who speak in phrases or dependent clauses.
People who write well tend to be able to compose not in words or even in sentences but in phrases that come to mind. I do not think in words. That would be silly and would result in a fairly scatter brained approach to both thinking and writing. And I do not usually think in well developed clauses. I usually do not know, for example, how a sentence is going to end when I have begun writing it. My mind thinks phrase by phrase. It might have words at its disposal and some notion of what kind of clause is going to come out at the end of all this cognition, but my thoughts tend to find themselves connecting phrase to phrase.
The centrality of phrases in thought can probably best be seen in the corrections we make to our own writing. There are usually a few errors in usage or spelling we correct as we compose, but it is far more common to erase or move or add whole phrases.
For this reason I see grammar instruction as misguided when it spends so much time on correcting the usage of words rather than the composition of phrases. We focus too much on the correctness of words rather than the style of the clauses and phrases that we write. Our thinking and our selves are not so well shown by the words we choose as they are by the phrases and clauses we use.
By moving away from words and on to phrases and clauses, we cannot get away from the issues of style that these units of writing bring up. It is in style that we probably have a better chance of getting students to think about how they think and how they write. Word choice has a good deal to do with style, but words also bring baggage with them. They are more often going to be corrected for being right or wrong. If we spend more time on phrases and clauses, we can spend more time on style and how it affects the reception of our writing. Style becomes the organizing principle of grammar.