SOLVED Phantom Phone Calls From Weird Extensions

[PBXMePlz]

So this phone on my dev environment has started to receive phantom phone calls from weird extensions that don't exist in the PBX. The calls also don't show up in CDR, so I'm kind of thinking it is network related, but the other phone I have on my nextwork in my production PBX is not receiving the weird calls.

Given the model of the phone, I'm wondering if there's a config item I need to set that would help fix this. The phone is a Grandstream WP820 (I actually hate this model btw, just not good call quality over wireless).

Thoughts? Ideas?
Since it's not production, it isn't a huge issue, but when/if it ever happens in production I would love to know the cause/solution.

 

[Adrian Fretwell]

Don't work with Grandstreams but Yealink phones have settings called: Accept SIP Trust Server Only and Allow IP Call that help prevent this from happening:

 

[PBXMePlz]

I think for Grandstream, or at least this particular model, it is probably this one.
The common Grandstreams seem to already have this enabled, but this one in particular is probably a forgotten model, for reasons I've mentioned.

Thanks for your help @Adrian Fretwell