How can I activate the call log on my iPhone?

Here are some things you can try if your iPhone call log has disappeared:

• Check your settings 
• You can try going to Settings, then General, then Reset, and then Erase All Content and Settings. Then, follow the on-screen instructions and choose Restore from iCloud Backup on the App & Data screen. Sign in to iCloud and select an iCloud backup from the list. 
• Check your call history 
• You can open the Phone app and tap Recents to see a list of recent calls. You can also delete your entire call history by tapping Clear, then Clear All Recents. To delete a single call, you can tap the Delete button, then Delete. You can also swipe left on the call and tap Delete.