Bass cello regularly left in ring (4)
I believe the answer is:
bell
'ring' is the definition.
(both can mean to call on the phone)
'bass cello regularly left' is the wordplay.
'bass' becomes 'b' (musical abbreviation).
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
'left' becomes 'l' (common abbreviation).
The alternate letters of 'cello' are 'el'.
'b'+'el'+'l'='BELL'
'in' acts as a link.
(Other definitions for bell that I've seen before include "Scottish-born inventor of the telephone, d. 1922" , "Alexander ..., inventor of the telephone" , "He invented" , "pen name" , "Something to jingle?" .)