Phone showing ss# has been linked to the dark web

This is not an issue with security on your iPhone. A major data house who stored personal data including Social Security numbers was hacked and the data of billions of people was obtained by the "dark web". What you need to do is contact the three credit reporting agencies - TransUnion, Experian, and Equifax - and put a credit freeze on your account. Then closely and regularly monitor your financial accounts.

For more information on the data breach, see:

https://www.cnet.com/personal-finance/check-if-your-social-security-number-is-in-of-the-national-public-data-hack/

Regards.