Here is an issue I ran into using my Grandstream GXP2140. I used the “Otherwise” and that fixed the “ghost” calls.
The options available will depend on the model of your phone.
Under Settings -> Advanced Settings check for an option to “Disable Direct IP Calls”
Under Profile/Account set Check SIP User ID for incoming INVITE to Yes.
Otherwise please open Account x -> SIP Settings -> Security Settings and set the option Accept Incoming SIP from Proxy Only to Yes.