Q: Can I remove all pictures from my iPhone via Photos on my Mac

With iCloud Photo Library

Get help with your iCloud Photo Library - Apple Support

Hope this helps

You can delete photos and videos selectively using the included "Image Capture.app" application on your Mac.  However, I am doubtful that you can replace a video withought instead using iTunes to sync it back to the device.

Depends.

If you enabled iCloud Photo Library then absolutely NO. Deleting photos anywhere will delete them everywhere.

If iCPL is not enabled, you can continue to use My Photo Stream to sync new photos to your computer and use iTunes to control which photos or albums you want on your device.

Photos User / Help guide:

https://help.apple.com/photos/mac/1.0/?lang=en

Using ICPL you would delete them everyplace not just on the phone - it syncs to keep all libraries exactly the same - every addition, deletion and edit is made everyplace not just on the iPhone

LN