cannot log into iphone to erase

Be sure you are following the instructions found here: How to Erase (and restore) your device to factory settings)

 iPhone, iPad, or iPod Touch https://support.apple.com/en-us/HT201274

And are you sure you have entered the password that is associated with the Apple ID shown on your phone? If you can't do so, then you have a significant problem and probably will be unable to use the phone. Post back if you need more help.

Do you have access to another WiFi network where you can try? That has worked for several people.

Try a restart.

Restart your iPhone, iPad, or iPod touch         

Try a forced restart.

Reset Device.      

If necessary

Hard reset.        

Do a backup and try a factory reset. Then restore from your backup.

Restore to Factory setting.      

Backup - Restore your device from an iCloud or iTunes backup.