Phones with Android operating systems use MP4 as the video formatting, so if you're using an Android phone, you will not need to convert.
iPhones, however, use MOV as the video formatting, so you'll need to convert your movie to an mp4 format. Here's an easy (and free!) way to convert your file:
Go to https://www.nchsoftware.com/prism/index.html and click on the "free version available" link in the fourth bullet, circled in the image below.
Download and install Prism.
Add your file using the + (Add Files).
Make sure the "output format" toward the bottom of the screen is set to .mp4.
Make sure the "save to folder" option is appropriate for your computer.
Click "Convert" and once the conversion is complete, your .mp4 video should be in the assigned folder.
To convert your Powerpoint project to MP4, simply export it and choose mp4 as the file format.