Talking about restoring iPhone, you have two options: restore from a backup file and restore iPhone to factory settings.
While restoring from a iTunes or iCloud backup, both iTunes and iCloud will remove all the data on your iPhone, photos, text messages, videos, and everything. Then, they will import all the data from the backup to your iPhone. So, we can say yes, it will delete everything on your iPhone.
And restoring your iPhone to factory settings simply will erase everything - data and settings on your iPhone.