Ok... i'm going to be nice about this. I'm a 55 year old woman with plenty of life experience. I also very well understand the nature of men.
Men look at women, porn, have sexual thoughts frequently, all because of the male sex hormone, testosterone. It's a very powerful hormone which causes men to be visual sexual creatures. A man who looks isn't disgusting or a freak, and he's not trying to become that way -- it's just his nature. Men oogle over naked women because it's what they were designed to do. When it comes down to it, Mother Nature designed the man to be prepared to spread his seed as often as possible... and the fact that a man is tired and falls to sleep after sex is part of this too. His body releases a hormone after sex which makes him tired, so he can get rest for "the next encounter". On the other side of the coin, women are more selective about a partner, and it's not just the penis or his body that attracts us most of the time. There are many, other important factor. Women look to see if the man would pass on strong genes and would be a good provider, even though looks and physique are important, the are not primary in a woman's mind.
Just because a man is married or has a partner, doesn't mean he's not going to look or fantasize. It also does not mean he doesn't masturbate, because most men who are attached and have a good sex life, still masturbate. Again, this is just their nature, and has nothing to do with the quality of his personal sex life.
I'm sure that, if you have computers or laptops at home, your husband already has constant access to porn. So a phone with a data package isn't going to be any different.
Perhaps you can accept these facts of life, and let your husband indulge in fantasy. It's not going to hurt anything. And i have yet to hear of a man who looks at porn or pics of a naked woman and then rushes out the door to try and find her!! It doesn't happen.
I did my research about all of these things years ago after i had a high testosterone pregnancy. I can tell you that, if you're not used to testosterone rushing through your system, you're in for a huge shock. All i thought about was sex. When a man walked by, i often wondered what he looked like naked or if i could have sex with him. I sometimes had the urge to masturbate in the strangest places (but i did issue control over that, although it was excrutiatingly difficult). I even talked to the doctor about it, and he said this, "you have a very high testosterone pregnancy. Now you know what a man goes through during the course of a normal day".
I was never so happy the day that pregnancy was over!! It was difficult. I'm not a man, and i'm not used to feeling like that!! I did for six months, and now i "get it".
As women we have to realize that men and women are different in many ways. And our sexual natures are one of the biggest differences. It's ok, we have all survived these differences for thousands of years.
My advice is to accept your husband's male nature, and stop stressing out because of it. Perhaps practice acceptance because you're never going to change his nature. It's just not going to happen.
I hope this helped in some way.