i want to erase all content on my old phone but the screen is broke and i cant do it from the phone is there another way

You can erase your phone remotely using FindMy from another Apple device …

… or from https://www.icloud.com/find from any web browser.

YW.

FYI, the following article provides a good checklist of steps which should normally be performed prior to disposal of a device.

https://support.apple.com/en-us/HT201351