how to unlock the phone

It sounds like your phone was reset between when you lost it and now ???

See this: How to remove your iPhone, iPad or iPod touch passcode without a computer – Apple Support (AU)

You WILL need your AppleID and password.

If your iOS was prior to 15.2, you’ll additionally need a cable and a computer to follow the steps linked near the bottom of the article.

There are different kinds of locks. What is the message that appears on the screen of your phone?

You should only need to enter your passcode.

Are you seeing something else?