The number of erase cycles very much depends on the type of flash used. Single level NAND typically have 100k+ erase cycles whereas it's ~10k for multi-level NAND. As a rule of thumb, MLC is cheaper and higher density than SLC.
NAND controllers - whether implemented in software or in hardware perform wear-levelling, bad-block management and error correction, and some erase units are held back to replace blocks deemed to be beyond salvage.
There are a number of possible hardware architectures for attaching NAND devices in phones.
Apple is hanging (what I assume are) MLC devices directly off the applications processor.
A more common scenario in Android phones is to use a smallish NOR device for the bootloader and kernel and then an eMMC NAND Flash device with the ext4 filing system for everything else. eMMC is essentially the same silicon as removable media card. but packaged for direct mounting into a device, with embedded NAND array management.
in either case, the underlying NAND performance is considerably abstracted from application space. When you consider that MLC-based SSD devices are marketed at enterprise users who hammer them, any load generated on a smart-phone is unlikely to be a concern.
