The OP compared a Leica, which is full frame and also very expensive, to an iPhone. I'd take an entry level full frame camera over an iPhone, just because it's the same sensor size as a Leica, but not in the same price bracket.
But yes, I'd also take any "full sized" camera over an iPhone in terms of ergonomics, resolution, etc. I do have an APS-C body that blows my iPhone to smithereens. I've never used a MFT camera, but am sure it would be better than a phone also. I said full frame just to keep the conversation relative to the original question.
Basically I'd take anything over an iPhone personally.