I googled "sentence fragments" which appears to be an Americanism, which Peggy doesn't seem to know either.
It is what the rest of us call an incomplete sentence. Which to my mind describes the issue far better.
No, to my knowledge, Pages doesn't detect those. Probably because they are obvious to a cursory reading which is always the best method of sub-editing.
If you are unable to detect such elementary examples of poor English, I'd say it is time you abandoned English, and all who sail in her, and take up another language. Grunting and pointing comes to mind.
Peter