Hello, beech_.
After reviewing your post, it appears that the contacts on your iPhone 11 are missing after you deleted your Yahoo email account. We're glad to help with this.
What does iCloud back up? -- It sounds to us that your contacts are in your Yahoo account, and iCloud doesn't back up anything that's stored elsewhere.
Add an email account to your iPhone, iPad, or iPod touch -- Check for you contacts in your Yahoo email account using the webmail site. If they're there, you can re-add the account to the Mail app on your phone.
Set up and use iCloud Contacts -- If you're using your Yahoo email account as the primary address of your Apple ID, turn on Contacts for the account and they should sync. After a bit, log into icloud.com to make sure they're syncing.
If your iCloud Contacts, Calendars or Reminders aren't syncing -- If your contacts still aren't automatically syncing, the steps in this article can help
Take care.