My first question would be:
Is the information, interaction, and navigation equal on all devices?
If not, it's definitely better to use different profiles.
If yes, still my answer would be the same. As creating responsive pages and device specific pages mixed and microflows opening device specific pages will lead to spaghetti.
Especially the way you phrased your question, it seems that there is not a very clear picture on scope. Thus, I expect that device specific requirements will come, and as a result of that, different interaction, information, and navigation. So better start right instead of starting quick and have a headache refactoring.
Imho you should always design different screens for phones due to the smaller screensize. Tablet and desktop most of the time could use the same page. So I would design both paths from the ground up. Or start with responsive first and then do a redesign for phones. Some stuff is just never doable on phone so you have to decide which functionality you want to give mobile phone users.
Great answers by Rene and Ronald. One addition: pages are hard to design if used on web, tablet and phone, but with having three pages for the same functionality, also beware of duplicate functions on documents. Chop up pages-fragments into snippets that you can use on any type of page.