You should use Bold, Italic and underline on your keyword phrase in every post and page. Try to use all 3 but don’t overdo it and mark all your keyword phrase appearances inside a post or a page. Make sure to use all 3 at first and for every additional 100 words inside your page or post use one of the three again and so on. I mainly use underline and italic once and I use bold once for every 100 words.