This is misunderstanding the purpose of the restriction.
The main reason not to bring a phone into the room is that the phone could be compromised. If the person is compromised then a device isn't your problem, because they could view the documents and copy them on paper or just remember the contents to write down later.
In a corporate environment no-camera/no-phone policies are sometimes also used for DLP reasons, out of expediency. Oftentimes it is more profitable to hire less trustworthy people (read: cheap labor) and simply make it inconvenient to steal data. This usually works good enough when you're trying to protect widget designs and not human lives.
Most people can take more photos then they are capable to memorize.