I used this method to check some of the lights in my house a few years ago. The slow-mo video mode on my phone used a rolling shutter which captures one row of pixels at a time, meaning you could see the flicker in part of the video, even when it’s a multiple of 60 Hz or above 240 Hz. The flicker and camera frequencies also aren’t exactly synced up, so you can see the dimmed parts move across the screen.

You can get a pretty good idea of frequency, depth of flicker, and if the LED’s colors are flickering in sync from this, and I can confirm that Philips LEDs, specifically the EyeComfort series, are good.