The sleep/lock button (also called the power button) on an original iPhone can wear out over time, especially with heavy use. Replacing it is moderately difficult and requires disassembling the phone. You'll need specialized tools (e.g., Pentalobe screwdriver, suction cup, plastic prying tools) and a replacement button. If you're not experienced with phone repairs, it’s best to have it done by a professional, as the process involves delicate components like the screen and battery, which could be damaged during disassembly. If your iPhone is out of warranty, many repair shops can replace the button for a reasonable price.