What's pointing to the NX being a phone?
First, just look around and see how huge mobile games have become. Games like Clash of Clans can afford to put A list actors in their commercials.
Second, If nintendo was going to pump out a stronger home console they would be directly waging war with xbox one and PS4. Right now Wii u isn't really doing that it's kind of it's own niche market. Just from what I've seen from working retail. Nintendo has establish a nice little network with 3ds and wii u. I can see them adding to it.
But directly trying to compete with XB1 and PS4 would mean better hardware. Most notably blu ray, which Sony own. Microsoft is taking it in the rear for every console sold and probably games too. We know from past nintendo isn't willing to do this. That's why we ended up with small philips disks on GC. I don't think nintendo is lined up to try to sell us a 4th DVD based console and try to push it as cutting edge.
Third, Nintendo has thier first ever app coming to mobile platforms and its not a "video game" really.
http://www.cnet.com/news/nintendos-first-mobile-game-miitomo-isnt-exactly-a-game/
They're probably saving their real titles for their specific device. Which will probably be a power house of a phone. Get big money contracts going with mobile phone carriers like T-mobile to have this phone only be on their network. Similar to Iphone and at&t at first.