Feeling lonely whilst in a relationship

I'm not wanting to moan about my partner as he is a really nice guy and so much is good about him. However, I do find that sometimes I feel lonely and left out. We have been in a relationship for over 2 years... Its just the two of us as our respective kids have left home. But it's actually now just the two of us, it's me and then him and his phone. It's like a third person in our relationship and it always gets his attention from first thing in the morning until the last thing at night! Don't get me wrong I have a phone and use it but I choose to when I'm not going to ignore the company I'm in. We can be day on the sofa, I'm just in from work, he's retired, and we'll be chatting and then all of a sudden he'll switch to his phone and starts scrolling Facebook right in front of me and he won't say a further word to me for 15 minutes or longer. He'll do this when I'm company of family too. Just sits and scrolls whilst everyone chats and connects. I'm trying to work out why he goes this but I can tell you it has an impact on the people around him. It's like he chooses to ignore us and prefers the company of strangers online, reading about their virtual lives or watching stupid videos. Again, we all do that but choose a more appropriate time. I've tried talking to him about it but he gets very defensive. He's nearly 53 and I'm 52. Is this how modern life is? I want to make the most of being with my partner but this behaviour just makes me feel lonely and pushes me away to find others for human interaction that I want with him.