The Razer Phone is one of the only devices in the current mobile market to feature a 120Hz screen that can display content at up to 120 frames per second for buttery smooth videos and games, but Sony apparently planned and scrapped the feature for a number of its Xperia smartphones. The initial discovery in its practical form was made by a developer on the XDA Developers forum by the name of uditrawat. Thanks to Sony's Open Device Program, uditrawat was able to dig up a kernel commit that mentioned and subsequently blocked a mode that ran the Xperia XZ Premium's screen at a 1080p resolution and 120Hz refresh rate, then revert that commit in a custom build of Android 8.1 Oreo for the phone.
While testers of uditrawat's original build of Android 8.1 widely reported that the new display mode did not work as intended, some users decided to try recompiling the kernel in the same way for a build of Android 7.1 Nougat, and some of them found it to be working just fine. Success or failure seemed to be somewhat random. It was later found that the screen mode was present in most newer Sony phones, except for the Xperia X Compact. Reportedly, what's actually broken is the toggle to turn that display mode on; according to XDA user Myself5, if a way to enable the mode by default at the kernel level were found, there would be no reason, theoretically, for it not to work. That's not to say with any degree of certainty that the screens on these devices are actually physically capable of such a high refresh rate, but more digging around in the kernel, or an official update from Sony, could give a definitive answer in the near future.
The Razer Phone is aimed at gamers, who naturally value a high refresh rate for clear and smooth action that they can react to quicker, and is thus claimed as the very first phone in the world to have this feature. The Sony phones with this display mode hidden away would not technically be able to strip Razer of its crown, since the feature was disabled by default, but it would be a pleasant surprise, to say the least, and may well open the way for other phones with AOSP-built ROMs in community development to see if their devices are capable of running at a higher refresh rate.