The Phone caddy will fit the 6 plus easily if inserted vertically oriented. I don't use the caddy in that way (it is the place I stash pocket change) but I am certain the 6 plus will fit.
I actually mount my 6 plus with a different system extending off the central stack. I love my CCI and Evannex have incredible service. They took back the first CCI I ordered after I found out they had a Carbon Fiber version, even though I had the first one for a couple of weeks. The folks at Evannex are great!
Peace,
Father Bill