iPhone storage is full. Now it won't turn on.

There is a plethora of information on the internet on what to do when your storage is almost full. But no information on what to do once your phone has no more space and will not start up.

I can get to the apple icon on the screen but it just sits there for hours. I can reboot using the side keys but get the same thing each time.

I tried connecting to my computer and opening the data from there. It shows 0gb free. I cannot open the files from there.

I have tried to open the phone via iTunes but it gives an error saying iTunes cannot access my phone.

First question is, can I start the phone without losing any data?

If necessary, how do I reset the phone so I can turn it on and begin the process of restoring it?