Having a bit of a weird problem here, People are trying to call EXT 140 on the freepbx server internally and they are getting put through to an outside number. I’ve check the Grandstream gxp2140 that the extension is linked to, and there are no speed dials listed in the Asterisk Phonebook.
The call isn’t registered on the 140 phone as being received and the 140 extension can outbound calls so it’s not a problem with the phone itself.
I have had this issue prior with some Mitels. I know you said you did not think it was the phone, but make sure the end user did not forward the phone in the hard phone itself.