Most likely spam. I didn't answer, and they didn't leave a message, but I looked up their carrier (Brightlink Communications) and found a warning letter that the FTC sent them for violating laws related to telemarketing and robocalls. The FTC warning letter for anyone interested: https://www.ftc.gov/system/files/documents/foia_requests/Brightlink%20Communications%20LLC%20Warning%20Lettter.pdf