As per the patent images, zirconia could be used for the back plate of the iPhone, with a circular centerpiece reserved for the Apple logo. The matte finish would correspond with a Pro/Pro Max model, and would definitely suit their more premium role in Apple’s lineup.
Apple’s patent images reveal which aspects of the iPhone and Watch might use zirconia
What’s zirconia, exactly?
Why would Apple be exploring ceramics, zirconia in particular, instead of sticking with glass and metal, the de facto standard materials used in the industry right now? See, the industry is always trying to one-up itself with sturdier and lighter materials that can also survive an unfortunate rendezvous with the ground, while also remaining visually pristine by preventing scratches.
It’s stronger than most common metal alloys and offsets the effects or regular wear and tear. It’s actually one of the dentist industry’s favorite materials when it comes to artificial crowns, because it has so many physical advantages over other materials. It has also dethroned aluminum oxide as the material of choice for artificial hip joints and other implants.
Image credit — zircon-association.org” 
What’s the downside we mentioned earlier? Well, given its much superior quality in comparison with most metal alloys and glass that usually make up the exterior of a modern smartphone, zirconia is noticeably more expensive to produce, which could be another catalyst for a future iPhone price increase… Still, there’s the possibility that Apple might not use pure zirconia, but instead add it to aluminum or steel alloys, which would still greatly improve their mechanical properties and overall resistance.
And that’s exactly what Apple hints at the patent description, stating that “zirconia-based component may be formed of a ceramic such as a partially stabilized zirconia ceramic or an alumina toughened zirconia ceramic”.
Ceramics as the future of phones
And let’s not forget that ceramic and iPhones are not exactly strangers. Both the iPhone 12 and iPhone 13 series both come with Ceramic Shield displays, offering up to 4X better drop-resistance in comparison with previous iPhones.
In the end of the day, it’s merely just one patent, so there’s a pretty high chance that Apple never actually decides to utilize it, with a ceramic iPhone remaining a pipe dream of some, this author included.