Currently, the highest-res smartphone image sensor in existence is one of 108MP. Obviously, it is used as a marquee feature on the back of devices like the new Xiaomi Mi 11. However, should the prolific leaker Digital Chat Station be believed, it might migrate to the front of upcoming models soon.
https://www.notebookcheck.net/Smartphone-selfie-cameras-will-upgrade-to-100MP-or-more-soon-new-leak.521400.0.html