i hadn’t heard of it before but i found a verge article that says

The battery regulation contains an exemption for devices “that are specifically designed to be used, for the majority of the active service of the appliance, in an environment that is regularly subject to splashing water, water streams or water immersion.”

the actual legislation (linked in the verge article) says

… this Regulation should provide for a limited derogation for portable batteries from the removability and replaceability requirements set for portable batteries concerning appliances that incorporate portable batteries and that are specifically designed to be used, for the majority of the active service of the appliance, in an environment that is regularly subject to splashing water, water streams or water immersion and that are intended to be washable or rinseable. This derogation should only apply when it is not possible, by way of redesign of the appliance, to ensure the safety of the end-user and the safe continued use of the appliance after the end-user has correctly followed the instructions to remove and replace the battery. Where the derogation applies, the product should be designed in such a way as to make the battery removable and replaceable only by independent professionals, and not by end-users.

im far from being a legal expert and i know apple has its own private army of lawyers, but it seems like it will be an uphill battle to say the iphone qualifies for that exemption.