I wouldn't count my phone or my iPad Mini on my total, even though they could obviously be used for that. I initially didn't even count my Kobo Arc either, since I still view that as a tablet... Instead, I qualified my eReader collection based on eInk devices only:
1. Kobo Mini (my first eReader)
2. Kobo Aura HD
3. Basic Kindle (7th Gen)
I did a big clearout of my collection over the past 12 months... Previously I would have fallen into the 5-10 device category as I also had a second Kobo Mini, a Kobo Touch, a Sony PRS-650 and 350...! It is time to spend less time collecting devices and more time reading! This year I'm finally starting to explore our local library's eBook catalogue.