iPhone 11 Pro Max video specs for export

To try and approximate the file size and quality of the original, with the intention of editing it further, you could use Adobe Media Encoder to transcode the video and new audio track to one of those high-quality intermediate file formats that's used for editing (not final distribution), such as a form of Apple ProRes. I'm not sure exactly what the right numbers would be, partly because I think the format, bit rate, etc. that the iPhone saves might vary depending on the pixel dimensions (720p/1080p/4K) and type of video (normal, HDR, slo-mo...) the iPhone was set to capture. The fact that the filename ends in .mov is not necessarily helpful, because .mov is a container that can hold many video formats.

Another approach to this is to try a conversion utility that has a "pass through" option, which means to leave a track unchanged. For example, you could set up a video file so that the audio is replaced with a new file, but the video is "passed through" without alteration. I don't think that's possible in Adobe software, though I could be wrong about that. Below is an example of setting this up in the ffWorks utility. ffWorks is paid software, but you get a number of free renders before you have to pay. I've tried to set up pass-through in other free utilities such as HandBrake and VLC, but it either isn't as straightforward or doesn't work as well.