How can I tell if my phone has been hacked

If you’re not an investigative journalist or political dissident or someone with access to classified or sensitive or vast financial info, or similarly interesting to folks with a whole lot of money, any sort of hack here is very unlikely. Not impossible, but very unlikely.

What to do? Start working in your own security. (We ourselves tend to get “hacked”, less commonly our devices.)

• Recognize and avoid phishing messages, phony support calls, and other scams - Apple Support (some of how we ourselves can get “hacked”)
• Settings > Passwords > Security Recommendations, check through and clean up any issues found
• Enable two-factor authentication, if that is not already enabled. That gives you one last chance to keep control of your Apple ID, if the password becomes known.
• Use the built-in security and privacy protections of iPhone - Apple Support
• Personal Safety User Guide - Apple Support

As long as you gave them none of your personal information, you did the right thing. Sounds like spam not hacking. Take a good look at this link...

Recognize and avoid phishing messages, phony support calls, and other scams - Apple Support

iPhones are not easily hacked. What makes you think yours has been hacked?