The problem is that even the manufacturer get this wrong all the time. IP68 does not mean "Can be used in swimming pool" in real life - it means that under exactly controlled conditions, the device can stand submersion in water. True, the "8" should mean that the device is hermetically sealed, or that the ingress of water does not cause harm to the device. However, this depends on many things, and should not be taken literally. Especially because you cannot provide controlled conditions - for example, the temperature of the water and of the device are to be identical, and the device must not be moved or pressed against something.
So, in real life, an IP68 phone is totally safe to be used in the rain, or when it falls into water - if the rubber flaps are exactly in place, an the rubber gasket in the SIM card bay is not wrinkled/overstretched by to strong tightening of the screws, that is.