Modern is as Modern does, so forever shall confusion reign!
A phrase used to be a phrase, a clause used to be a clause, and a sentence used to be a complete thought. Those days are long gone! There are now so many re-interpretations of so many supposedly 'pointless and useless' grammar rules that everything that used to be known is known no longer. I can not see any progress in how students are taught English compared to how it used to be taught many decades ago.
English Grammar should never have become interpretative. It should be learned and used to interpret the meaning of sentences, and those sentences should be complete thoughts; else, what's the point?
Grammar should be learned from older books, and newer books should be used to create lists of newfangled terms simply so that you can pass a test. There are too many confused students. What do modern grammerians have to say about that? Good Luck. I suggest that you go to google books online and download free ebooks by Reed & Kellogg. They are clear and concise. Believe me, there's nothing new in grammar, just new opinions that confuse the people.