How to transfer videos from PC to iPhone?

I have some clips that I took with my Sony a5100. All the pictures actually were able to be transferred wirelessly from the camera to my iphone, but the videos require a USB cable to be downloaded, so I had to transfer them to my computer instead. I would like to get them on my iphone so that I can upload them to instagram. I tried using itunes, bluestacks, google drive, etc but nothing works. Is it the file size/type that is causing all these issues?

Using a USB cable, as you mentioned.

What file extension is it… Most phone / computers understand mp4… Mpeg4…

Just choose your desired program (iTunes or Syncios) to help you manage files in your iOS devices and PC. After that, you can fully enjoy any movies or music on your Apple devices anytime anywhere. Sync iOS devices like iPhone, iPad, iPod simultaneously with your PC; Transfer files between iOS devices and PC;