Software aside, the storage (NAND flash) in the phone actually does wear out and get slower with use. Given how many writes modern software likes to make, this

Software aside, the storage (NAND flash) in the phone actually does wear out and get slower with use. Given how many writes modern software likes to make, this can add up. But, critically, this wear doesn't just happen. It only occurs when the NAND is written to. It won't happen if software is effectively caching and combining writes.