The infrared port was one of the first ways for a phone to share data locally with other devices. For example, you could sync the calendar from your PC to your PDA over IrDA. It fell out of favor after the bugs and compatibility issues of Bluetooth were ironed out, but IR lived on. It was repurposed as a remote control feature, allowing phones to command TVs, air conditioners, anything with an IR remote, really. Infrared communication is so simple that it never suffered from the compatibility woes of Bluetooth. If anything, today's smart devices are a crapshoot - can your smart speaker...
Source: https://www.gsmarena.com/counterclockwise_old_tech_that_got_repurposed_for_new_features-news-36526.php
