How can I backup my iPhone 6

This document outlines the various ways you can back up your iPhone, iPad, and iPod touch --> How to back up your iPhone, iPad, and iPod touch - Apple Support

For iCloud backups the things you are mentioning are required.

Automatically back up with iCloud Backup

1. Make sure that iCloud Backup is turned on in Settings > [your name] > iCloud > iCloud Backup.
2. Connect your device to a power source.
3. Connect your device to a Wi-Fi network.
4. Make sure that your device's screen is locked.
5. If you get an alert says that you don't have enough iCloud storage space to complete the backup, follow the onscreen steps to buy more storage.

That is how iCloud automatic backups work. Are you saying that you cannot create a manual backup in Settings>Your Name>iCloud>iCloud Backup>On> Backup now?

Are you trying to backup using a hotspot?