Microsoft Teams Incoming call via Direct Route shows "Spam Likely" for 4-digit extension

I'd claim that this additional info comes with SIP from the PBX or PSTN provider as SIP Header From Display Name. Or you user contact object, saved in Outlook if it affects only a single user.

I think you cannot change this in Teams neither via Shell nor TAC.
You could check your SBC for Teams Direct Routing and configure message manipulations to remove this info in legit calls.
Or you might better ask your pstn sip trunk provider/pbx admin which is connected to your SBC to ask if they use some sort of spam call information tagging. Maybe your provider could turn it off on your pstn sip trunk. Otherwise you usually could do this on your SBC.