I replied to you on that thread. A lot didn't agree with me but my son is 19 (I am 37) and he still sees his dad at least once a week and they speak on the phone. From experience I personally wouldn't get involved with someone who had what I consider to be a poor relationship with their kids. It's always always for a reason and not a good one. Fair enough they don't see each other face to face but I would expect phone or email or text at least really. But we judge everything by our own standards and that is mine. Other people are different.
The calls? I always start relaxed and happy, how are you kind of things. Ask about their lives in the main. How their day was. This usually gives you follow up questions to ask. Without sounding like an interrogater obviously. Interested. Not Sherlock Holmes. Just breezy interested.
An example this week. Guy who was interested in the theatre, arts and all my kind of stuff. was good on email. Took my number. Text me to ask when he could call me. All good so far - respect and boundaries.
Phone call - I always have their profile up when they call. He had photos of cats. So I asked about the cats. He then proceeded to tell me all about said cats and how they were his babies etc etc. So I asked how he managed to go away on holiday? He doesn't. Was the answer. He won't leave them.
I am up for weekend breaks etc etc. This means him and I are incompatible for the long term. So I won't take it further. He's not a bad person, just not for me. Had I met him instead, it could have been a while before this all came to light given weekends away don't usually happen until a proper relationship is in place.
I ask about their job, their kids, hobbies. Just a friendly conversation for up to half an hour max. But its always very revealing. The friendly happy interested vibe relaxes them. So they open up and talk. And then I listen. Very carefully.
There is no set routine but after a few you just get better at it and what you are listening for. You need them to relax first though.