This isn’t necessarily true. LEDs are capable of running for years, but not all LEDs are designed this way or are operated this way. An LED in a given application can die quicker if:

• the LED manufacturer cheaps out
• the phone manufacturer runs the LED at higher current for more brightness
• the phone is poorly designed, allowing the LED to heat up
• the phone is exposed to significant heat and/or the LED is covered while used for a long enough duration