The 5.5-inch iPhone 6 might be called the "iPhone 6 Plus" according to Macotakara, a Japanese Apple blog with a mixed track record of getting the rumors right. There's also going to be a 4.7-inch version that'll just be called the iPhone 6.
We first saw the Macotakara report on BGR.
That's a deviation from standard iPhone naming. Apple usually distinguishes between models with a letter like S or C.
The report also says that the larger of the two iPhones will be available in the same color schemes as the 5S: silver and white, silver and gold, as well as black and grey.
As with most iPhone rumors, take this one with a grain of salt. But it does seem likely Apple will have to name its two new iPhones something different in order to avoid confusion.
We'll know for sure what Apple is calling the iPhone Tuesday.