I don’t currently have access to my PBX and I don’t use SipStation (which I think has special handling in FreePBX) but for a normal trunk you would set your context to from-pstn-e164-us to remove this.
See
If you have access to the trunk information for SipStation then set its context from-pstn-e164-us. If you don’t then please check for an option that let’s you change the format in which it return the caller ID.
It’s not suspect, it is just passing it in a different format, e164…
Re:
That “1” actually means it is coming from NANPA territory (ie, Canada, US, etc…), see