Make sure in Globals G01 – G05 (Miscellaneous) Telephone Remote Control is set to 1 = Local or 2 for Local nd Remote Control Enabled. If trying to connect Remote under Globals G29 – G42 (Special) you will need Rings until auto-answer set to a value 1-15. If you have an answering machine then one ring Greater than the Answering Machine and check Ring/Hang-up/Answer.
Is the phone service standard Plain Old Telephone service (POTs) over copper or Voice Over IP?