Copying is always safer, since you don't have to worry about something going wrong mid-transfer resulting from the loss of your files. If you had done this, you would (at the very least) still have the original photos on your device.
Please detail exactly what you did and what app you used to perform the file transfer.
On a side note, I always recommend using a cloud sync option, like Google Photos or Dropbox, etc. You never know when your phone might get lost, stolen, broken, etc, no matter how careful you are with it.