I do not have my phone on find my iPhone how do I erase it

Guess you could try a newer version of Wanted poster..

..with mug of 'Mr Missing iPhone' front and center.

Maybe offer a reward for him on milk cartons?

This topic question has come up before; the prevention

happens to work best, if done before the phone runs off.

We tried a leash on a one, but it chewed through.

If your iPhone iPad or iPod touch is lost or stolen - Apple Support

https://support.apple.com/en-us/HT201472

see second part of this article

Sorry to not have any ideas.

Have to set 'Find My Phone' first.

Or read article. ~ Protect your data.

Mine is acting up ~ and I wish it would run away..!🙀🎣🚀🌍

You can't. Since it not set up with Find My iPhone on iCloud, there is now nothing you can do with it in any way.