Hi messi20,
This can sometimes happen if your contacts are syncing with more than one account, such as iCloud, Google, or Outlook, and one of those accounts is overwriting the change.
A few things to check:
- Go to Settings > Apps > Contacts > Contacts Accounts and see which accounts have Contacts enabled.
- In Settings > Apps > Contacts > Default Account, make sure new contacts are being saved to the account you want, such as iCloud.
- If you use iCloud Contacts, go to Settings > [your name] > iCloud > See All > Contacts and make sure Contacts is turned on.
- Restart your iPhone and try creating a new contact again.
- You can also try saving the number directly from the Contacts app rather than from Recents in the Phone app.
If the contact still disappears after a few seconds, I’d also check whether the contact appears when you sign in to the account it is being saved to, such as iCloud.com or your Google/Outlook contacts. That can help determine whether the issue is with syncing or with the iPhone itself.
Hope this helps!