Given that the Osmo 4 will not work with the iPhone in a case, how do I attach ND filters to the iPhone?

Thank you,,

Hello there blucoyo. Good day and thank you for the inquiry. I hope that you can get the best information from our fellow DJI members who owns the DJI OM4 and uses an ND Filter on there mobile device. There is a possibility that it will work as long as the total weight does not exceed the limits of the OM4.  You may need counterweights for balancing the said mobile device. Thank you.

Counter weights are cheap on eBay,  also have a look at moment. they make a case that allows for lens etc to be mounted.

Thank you!!!!