Old-fashioned parent ringing teen on a regular basis (5)
I believe the answer is:
dated
'old-fashioned' is the definition.
(dated can mean old-fashioned)
'parent ringing teen on a regular basis' is the wordplay.
'parent' becomes 'dad' (dad can informally mean father).
'ringing' means one lot of letters goes inside another.
'on a regular basis' means one should take alternating letters.
The alternate letters of 'teen' are 'te'.
'dad' going around 'te' is 'DATED'.
(Other definitions for dated that I've seen before include "Antiquated" , "out of the ark" , "No longer fashionable or current" , "Went out with - old hat" , "Unfashionably old" .)