And broadly speaking by the cube of the distance from the source apparently. But in this case it decays from a mind-boggling starting level by everyday life standards.
If that camera is 5 meters away from the source the field there is still about 10 Tesla. I think that's about an order of magnitude more than most MRI machines for clinical purposes, and those already warrant a good deal of care with effects on metals.
MRI vendors require some parts be photographed at service. Standard tool for this is a phone camera. I don’t know if this applies above 3T but at that level it’s all fine.
And as for clinical field strengths - there are 7T scanners being marketed, but they are rare.
I personally don't work with machines like that, and never have, but I imagine most service would be out of the question without bringing down the magnetic field?
If the magnet is not active, certainly consumer electronics could be used even near it. If the magnet is active at anything close to it's operation level, I'm seriously skeptical that a cell phone would fare okay close to it. Have you tried for yourself? Are you sure that the photos you've been in touch with were not rather taken at about 0T ?
Nearly all service work is done with the magnetic field up as ramping down is a massive deal. iPhones and iPads work fine until very close and it’s what the documentation is kept on for the vendors I know (Siemens and GE, Philips use Microsoft gear). Philips require photos of the cold head, which is pretty close in. Get too close to the bore and they turn off for a bit, which is probably due to cutting flux lines quickly. Id suspect it doesn’t help their lifespan but I’ve yet to see it kill a phone.