Q: My iPhone4 is never backed up on iCloud

You must have iCloud Backup Selected on the iPhone.  Settings>iCloud>Storage&Backup>iCloud Backup. Slide right to Green or On

Do you have an active iCloud Account?  Is it linked to the correct phone number / Apple ID?  When you say you saw that no Backup has been saved in iCloud ...what and where did you see this?

iCloud: iCloud storage and backup overview

How do I make sure that my iOS device is backed up regularly?

You should be able to try a Manual iCloud backup by selecting that within Settings>iClould-Storage&Backup

not to be patronisisng, but you need to make sure you are connected to your wifi, the go settings>icloud>storage&backup>backup

if your wifi is on it should start to backup from the device to icloud.