Source? As another member alluded to, there are OLED TVs I believe support 12OHZ. So why would not a smart phone be able to support that?
OLED panels support 120 Hz but most TVs only accept 60 Hz input or at best 120 Hz at 1080p due to bandwidth limitations for HDMI 2.0. Phones typically have a much lower resolution so there is no reason other than development issues for it to happen. I don't know what are the differences besides size in developing TV scalers vs ones used in phones. It's probably not as easy as it seems as a lot of these panels are developed with VR in mind and it takes time for the tech to trickle down to more mass market products like phone displays.