I think a regularly scheduled time might work best. I'll suggest it the next time I talk to him.

He called about 20 minutes late. Only S5 was willing to talk. Phone rings. I hand it to S5 to answer.

S5 - Hi, Dad. Whatcha doing?

Dad - Cooking

S5 - Bye, Dad.

And he HUNG UP!

I stressed all day for a 30 second conversation.