Keyword-A keyword is essentially any word or phrase you use when searching with a search engine.” In a simple language, any single word related to your business, product/services which can be useful for your business.
eg. If you are selling shoes online then “shoes”, brand name like “Reebok”, “Nike” are your main keywords.
Keyword Phrase- Combination of those keywords is called key phrase.
eg. As per the same example for online shoe store above phrases can be (“Sport shoes”, “Reebok shoes”, “school shoes” etc.)
Your objective should be to rank on maximum key phrases for your website not just single keywords. As soon as you will start ranking on maximum phrases Google will automatically start showing your website for your targeted keywords.