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

Just checked the datasheet of the eMMC 5.1 used in my 2020 phone that I use daily now and it's MLC. It also has optional pseudo-SLC mode.

Only the very cheapest phones still have eMMC. I bought a Pixel phone second hand last year and it shows the wear level of the storage somewhere in the settings. I forgot the number but it was so low, extrapolation got me to something crazy like maybe 20 or 50 years of expected use at that rate

That consumer rate isn't datacentre use, but not every task is write-to-persistent-storage intensive. You can also replace the sdcard and write to that instead if this is a worry (that's what I've been doing on my phones since I use them quite intensively; maybe that's overkill nowadays idk)