How can I recover deleted photos and videos from my iPhone?

When you say you "deleted your phone", do you mean that you deleted your photos off your phone, both from the main library, and the Recently Deleted album?!? If you did that, you would have permanently deleted the photos.

If you were using iCloud Photos both on your phone and on your computer, you may want to check to see whether your computer has old backup copies of the photos in its Photo Library, as of a time BEFORE you did the deletion.

How did you perform the "safety copy"?

Photos can be backed up to a computer, backed up to iCloud or synced with iCloud.

If you synced with iCloud, you can see the photos in the Photos app at www.icloud.com

If you back up to iCloud, you cannot view the photos on iCloud.com but you can use the backup to restore the phone. See instructions in Restore your iPhone, iPad, or iPod touch from a backup - Apple Support

My iPhone started to restart itself every 3 minute

That is a serious issue that will require service at the Apple Store or authorized Apple service shop. The phone should have been serviced before you tried to do anything else.

So I did a safety copy of iCloud

How did you do this? I do not understand how this would be possible if the phone was restarting every 3 minutes.