The new iPhone Xs and Xr will use 35% post-consumer recycled plastic in their speaker enclosures, and 32% bio-based plastic for the the cover glass frame.
Apple is trying to avoid mining new materials and tries to find ways to use recycled or responsibly sourced materials,
Apple needs to make devices last as long as possible and make sure they’re recycled properly.
On 9 April 2018, the following info was published (see ref), we’re not sure if this is related. If it is, then we know that this was probably manufactured by Arkema.