It's not 'flashing'. It's in a boot loop. It starts to boot, runs into problems and then reboots.
So yesterday, after three hours, you probably had one random success in booting. Today, probably not so much.
What should you do?
Put the device in Recovery Mode or DFU Mode. Apple has instructions on their website for how to get in to recovery mode, and Google will bring up DFU Instructions. Connect your device to a computer running a fairly modern OS and have the system upgrade and restore your iPhone. Then setup your device again.
But…"That's going to wipe out all my data!" I can hear you thinking. Yes, it will. So, anything you did NOT backup before all this started is going to be lost. And that's the choice you have. Get your device working again and lose data, or continue to let it sit there trying to boot over and over - and not have access to your data because your phone isn't working.
Your entire problem stems from not having enough space. How do I know that? Because if you don't even have the space to download and install an upgrade, you don't have enough space period.
You could take this to Apple. I could be wrong. I wouldn't bet on it.
