Reddit reviews Neewer 37mm Clip-on ND 2-400 Cellphone Camera Lens Filter Kit: Adjustable Neutral Density Filter with Phone Clip for iPhone X 8 plus 7 Plus 7 6 6S Plus Samsung HTC Motorola iPad and Other Smartphones
We found 3 Reddit comments about Neewer 37mm Clip-on ND 2-400 Cellphone Camera Lens Filter Kit: Adjustable Neutral Density Filter with Phone Clip for iPhone X 8 plus 7 Plus 7 6 6S Plus Samsung HTC Motorola iPad and Other Smartphones. Here are the top ones, ranked by their Reddit score.
KIT INCLUDES: (1)ND 2-400 Filter, (1)Phone Clip, (1)Small Portable Box. Note: The smartphone is NOT includedADJUSTABLE ND FILTER: Reduce the amount of light reaching the film without affecting the color; Can be used to enable slower shutter speeds; Adjustable form ND 2 to ND 400 to meet your different needCOMPATIBILITY: With the phone clip, it fits for almost all the smartphones; Compatible with iPhone X/ 8/ 8 Plus/7 Plus/7/6/6S/6 Plus /6S Plus/5/5C/5S, Samsung HTC Motorola Tablets iPad and other smartphones; Without the clip, it can also work with the DSLR cameras with 37mm lens threadAPPLICATION SCENE: Perfect for shooting water flow, traffic flow, ocean, clouds, human stream and other moving photographyPORTABLE AND EASY-USE : One step clip-on design, easy to clip the lens stably and securely on your device for instant use; You can take photo with your devices at any time, travel with this lens at ease
I think you need a Neutral Density (ND) filter. They make them for phones
Check here
I actually bought this ND which is pretty simple if you're interested but then I found these adapter rings and realized I could use my nicer full size ND.
You will need this rig with the mic: https://www.amazon.com/Movo-Smartphone-Shotgun-Microphone-Samsung/dp/B077YS5ZV5
and also a clip-on variable ND filter (so you can control the shutter speed more, for a cinematic effect): https://www.amazon.com/Neewer-Clip-Cellphone-Camera-Filter/dp/B074JYY9Q3
Optionally, a tripod ($20), if you want some static shots without wobble at all.
And of course, you will need to purchase the app Filmic Pro ($15 with the needed in-app purchases), which is the best recording app for the iPhone. It's the same app used when real movies are made with the iphone (e.g. by the Sodebergh director).
Overall, $100.
Tip: if you want to add some artsy aesthetic, you can download the super 8mm emulation app which shoots video as if it was a film camera. Very convincing effect.