The management of Nintendo is the Board of Directors and Iwata himself. If the board of directors is unhappy, they could vote to remove him at any moment. If they really wanted to start making smartphone games for that kind of money, they would have fired him years ago.
Unless this rumor is talking about the top game designers, which makes even less sense. Many of the top designers have been given more freedom then ever these last several years since Miyamoto has become less hands on. There's a reason why a lot of recent Nintendo games have higher production values and orchestrated music compared to what they used to have. If the developers want to start making smaller smartphone games, they sure aren't showing it.
So yeah, the rumor is bullshit anyway you look at it.