Being apart from the grandchildren

Smileless,

It is not just a phone call.

That scenario assumes that ex dil can answer the call, has time to facilitate the call between the OP and gc or time to tell ex mil that is not a good time.

That scenario assumes the gc are available has no distractions so they can talk to grandma and they are in the mood to talk on the phone.

So no, just a phone call assumes availability of all parties involved.

Ex dil is the parent with the majority of custody in this case and I am pretty sure she has a thousand other things that have higher priority than being available on demand and drop everything when grandma calls.

Yes Hithere it is just a 'phone call.

Why is the ex dil expected to maintain the relationship? Does the son call his ex's parents and maintain their relationship with the grandchildren? Each adult child should maintain their family's relationships with the children.

If you read what the OP has posted Pnwmama you'll see that her son is maintaining her relationship with her GC.

The OP isn't expecting her ex d.i.l. to maintain that relationship, she doesn't want her to subvert it be refusing to allow her to talk to her GC on the 'phone.

Not allowing the children to talk to their GPs on the phone while they're in her care, knowing that her ex is more than capable of facilitating the relationship, is not "subverting the relationship". The GPs can accept that they need to have contact on their son's time.