No risk of that I'd say. Consoles are Nintendo's bread and butter, and SmartPhone games are more of a side-project. Super Mario Run on the iPhone was awesome, and I would buy other smartphone games from Nintendo if they ever made any more that were of game franchises I know and love from Nintendo. (But I'd never want smartphone gaming to fully replace consoles!) Nintendo make console games in ways that no other experience could ever replace! Smartphone games, while fun, are nowhere near as high caliber of an experience (simply due to the fact that consoles are designed specifically for that purpose, so there is alot more you can do with a console that you'll always be alot more limited on in terms of what is physically possible to create on a smartphone).
Sure, you can always add accessories to it in order to give it stuff that a smartphone doesn't have (like physical buttons, and motion controls, etc.). I saw in the Apple store the other day that such accessories already exist. But but being as you'd have to add accessories anyway in order to do that, you might aswell have a proper console that was designed for purpose. So there would be no point. It wouldn't make financial sense for Nintendo to do that either, as they wouldn't be able to sell consoles anymore, and would be just limited to accessories. (also software support is much more of a nightmare in terms of dealing with bugs when games are played on different hardware, whereas when it's designed for one specific console, this is much much easier for a software developer to maintain). So I honesty don't think we've got anything to worry about.
Nintendo Switch is a classic example of the fact that they've still got lots of lovely gimmicks that make their own consoles a little bit more special than anything a standard device could ever offer. They always put special effort into making their consoles more fun than just being a standard box with a bunch of buttons. So while people complain that other manufacturers make higher spec hardware, it's the innovation that always goes into a Nintendo product that makes the whole experience feel so much better than just doing what everyone else does.