Hello Carol7777. I have not the answer. However. I changed the titles on most of my hubs using Google's keyword tool as an aid when the ZzZ phenomena occurred. The views went from an average of mid twenties per day upward beyond 100 and remained constant after using the keyword tool. Or a 300%+ increase.
I realize it is a small number sample, yet results are results and relative to the marketplace, which for me today is Hubpages. More specifically it is to the followers that hub is submitted and their home feed. Word of Mouth occurs after that, since I really do not facilitate SEO principles, yet.
Yet, that does not answer what you asked regarding keywords and phrases. I am not a programmer, yet I have spent a portion of twenty years on researching reading. And the simple thing to remember is those web crawlers 'read.' Technology is amazing, however programmers are human and follow human rules with the assistance of technology when creating bots for a specific purpose.
A Catch 22 kinda' thing is, in this author's view from research is those bots do index our hubs, yet they do so for 'humans', not other bots. Learning how humans read for information, how humans read for specifics, and how humans read for pleasure becomes important how to use keywords with placement.
In other words the keyword search tool is extremely valuable. Yet, and maybe more so, is how those keywords are used is the key. With reading for information there is a methodology. Asking questions, like does repeating a keyword or phrase from the title in the bold text sub-headings more valuable? Is repeating the keyword or phrase in the media descriptor valuable? Is repeating the keyword phrase with the affiliate Market descriptor valuable? Is repeating the keyword or phrase with the associated links capsule more valuable? Is repeating the keyword or phrase with replies to comments valuable? And, I have always pondered synonym usage too. Or, what are those bots programmed for?
Bots do not have a conscious to my knowledge anyway. They only seek, find, and report back the information. That information is compared / contrasted to a matrix of some sort and the result is a classification. Then, maybe, that classifier is introduced to a larger matrix along with other classifiers. And, that result is an index of some sort. Again, I am only a novice with programming language.
This comment as a demonstration is 385 words with the keyword = keyword, which is used 11 different times or about 3%