A few years? I have a bunch of phones from 2009 around that are still fully working and I have never had eMMC fail on any of them, and they use it for swap among other things. In my experience screens, batteries and USB ports fail much more often.
Phone from 2009 uses SLC, or MLC with large SLC cache, thus capable of at least 10k FDW (full disk writes).
Modern phones typically use TLC or QLC within a inch of their physical limits (signal to noise ratio), thus qualified typically only up to 500 FDW, which translates into several years of use.
There are other mechanisms at play which further degrade this number, such as WAF (write amplification) and others
