This is exactly my experience with the 6+. Tried using it for a couple of months and it felt too big as a phone and too small for web surfing, PDF, etc.While I have an iPhone 7, my iPad Air 2 is still my preferred media consumption device.
Getting an iPhone 7+ would be a compromise--for me--on both fronts. It would be more cumbersome for the phone usages and a smaller screen for the iPad usages.
- I like my iPhone for convenience on the go, and for photos, and it's small enough to not be a bother.
- I like my iPad for streaming, internet, quick, photo editing, MRF, etc. the larger screen is just better.
That said, the 16:9 aspect ratio on the iPhone 6/6s/7 Plus really is much nicer for modern video content. A significant portion of the screen on an iPad is just letterboxing when watching HDTV content (1.78 aspect ratio) and practically half when watching most modern films (2.35 aspect ratio). For re-runs of Buffy, Charmed, etc, though, the iPad rules.