Phone crashed mid update

I was trying to transfer the information from an old phone to another one. I deleted the previous information of the "new" one, backed up the old one and then then began the transfer. The backup was done in finder on a macbook. When I then began the transfer it could not be done due to the "new" phone not being updated so I began doing that instead, via the computer. However mid update the update was "cancelled" and could not be completed which was also when the phone (an iphone 7) completely crashed. It can not be rebooted by pressing volume down and side button or be reached when connecting it to the computer. It will only flash the apple logo briefly when pressing the buttons and be loading for 10 min when connecting to the computer before it disconnects. What should I try next?