How can disconnect my iPad information from my iPhone

I had an iPad mini for a year now, my fiancé recently bought me an iPhone. So he told me I could since my iPad mini with my phone. But my mini is so full of storage, every time I plug in my iPhone it says it can't be backed up. But I want it to be. How do I disconnect my iPad mini info from my iPhone so I could back up my iPhone. Thank you all in advanced.