LFP is a type of lithium ion battery. Modern LFPs perform pretty well, though they're a bit worse than "regular" lithium ion, in part because they run at a lower nominal voltage of 3.2 volts rather than 3.6 volts. They're used in cars all the time, just not usually in the United States.

I've never heard of an LFP smartphone battery, but that doesn't mean it isn't done. I wouldn't be surprised if it was common in China.