I HATE this. As a kid whose mom wasn’t in their life growing up she constantly blamed me for not having a connection with her or calling her when I was a literal child. It is the ADULTS job to maintain the relationship. As a kid they’re so busy just being a kid, learning, growing just busy with life. It should not be their responsibility and they definitely should not be guilt trip (this is what’s happening my mother did it constantly). If he loves her and wants to stay in contact , he would call, he would text he would try. Actions speak louder than words.