Can someone explain difference of a responsive website and CP8 responsive limitations for phone?

Captivate offers a quick and easy way for non-HTML5-programmers to build a responsive elearning course.  However, there are always some compromises.  One of those compromises is that you have only three breakpoints to choose from.  One for desktop systems (up to about 1200 pixels wide), one for tablets (typically around 1024 pixels wide) and one for phones in portrait view (set by default to 360 wide).

The difference between this setup and a fully responsive website is that your web developer would probably be building it from the ground up in Dreamweaver using Bootstrap, Foundation or some other similar responsive framework and they would be able to program in as many breakpoints as they felt worth maintaining.  Then they would spend weeks of development time in the a nightmare of trying to replicate what Captivate does with just a few mouse clicks to create skins, themes, quizzes, animations, etc.

Compromise and prioritization of importance.  That's the difference. 

If saying your elearning course is "fully responsive" (meaning it has a breakpoint set up for each and every device viewport on the market) then hire yourself a programmer.  If using non-technical developers capable of making your elearning 'responsive enough' to be viewed on desktops, tablets and even mobile phones and releasing it as quickly as possible is more important, then use Captivate.