Oh i have had a similar problem, my daughter is now 6 and she still does not enjoy speaking to her dad on the phone. Sometimes she will just say "hello,goodbye"! I think daily phonecalls maybe a bit to much? We do it on a monday and Thursday and another on the weekend he does not see her. If she is watching tele i pause what she is watching, so she does not think missing anything. It is diffcult because really you cant force them to do anything they dont want. Maybe try setting a routine and have the same time and day each week. If there are less calls they will both have more to talk about. I know you said he does not really take your advice but suggest he tells your son what they will do when see each other etc
Hope this helps a bit x