I realize it's not reasonable to expect perfect spot color matches on a mobile device, even when calibrated with SpyderGallery.
But I am noticing that a few of my client's corporate colors are significantly off color, mostly in terms of saturation, in SpyderGallery.
Turning calibration off does not solve this issue, in fact it seems to make it worse. Is there an explanation for why some colors are less accurate than others?

There is a tendency to choose very saturated colors for corporate colors. Saturated spot colors, especially in the yellows and cyans, are hard for RGB-based displays to reach, and harder still for smaller gamut mobile devices. So warn clients that highly saturated colors in these areas will not display correctly, unless viewed on a wide gamut device.