While I can't condone grilling a child on what's happening at the other parent's home, at the same time I can understand where the child's father might be concerned for her welfare given the conditions she was living under with you previously. And since this is a pretty new situation, I'm sure that he's feeling very uncertain while she's with you.
As for a child whispering she loves a parent while she's on the phone, I see that regularly right here in our own home. Since the parents are in conflict, the child naturally feels that to say they love one parent will hurt or create a conflict for the other parent. The child doesn't need anyone to say anything to them to cause these feelings/fears, it can be just a natural consequence of being aware of the conflict. (Of course, it can be fed by a parent's actions too - but it doesn't have to be.)
And children acting differently after being with or talking with the other parent - again, completely normal and understandable - and the other parent doesn't even have to "grill" the child for it to happen. Over here, SD9 can have a completely innocuous conversation with BM but then be completely off the wall for a good hour afterwards. Again, a lot of it has to do with the child's own internal conflicts - and those are (can be) simply a natural consequence of the parents no longer being together.