It appears scammers are calling from 503 area code telephone numbers. The scammers keep calling but they do not leave a message. The calls seem like a One-Ring scam where cybercriminals trick potential victims into calling premium-rate numbers by ringing their telephone numbers once, hoping they will see the missed call and call back. The money collected via the premium pay-per-minute services will be paid over to the scammers unless the scam is detected and shut down by the callers' telephone service provider. The danger of these scams is not receiving the phone calls, but calling back the premium-rate telephone numbers.
The telephone that called me is:
If you have received a 503 area code scam call, please leave the telephone number the call came from in a comment below.