You would want a guy who has a lot of porn images of women stored on his phone to have an album of you on his phone? I don't know if that would really qualify as a compliment. If he sees these women's roles as display for prurient viewing, you really want to be in their company? You say she's "literally everything you are not"? Yes, she's someone who poses naked in porno shots, so men can look at her and think of her as body parts. And you are not.
In fact, it seems pretty usual for a guy to watch the occasional sleazy thing, but keeping lots of it around to look at over and over? For me that would make me wonder, how boring is his life, and how insecure does he feel about himself? I'd re-think a relationship with that kind of guy.
I guess I'd just ask him about it, like why does he have it? What does it mean for him, if anything other than she's a hot woman who takes naked pics?
As for her being everything you're not, I know it's hard to not fall down that hole, but remember that you're also everything she's not. She's not the one he loves, she's not the one he talks to, she's not the one sharing his bed, his life, his house (assuming you live together), his body, etc.
Maybe she's tall where you are short, is blonde where you're brunette, or whatever, has bigger or smaller or whatever breasts, is thinner or curvier, but remember that he chose you, and continues to choose you, just as you are continuing to choose him.
And Paxiled is right - she's all the way touched up and photoshopped. Her stomach is flattened, her legs are lengthened, her breasts are lifted, wrinkles and shadows erased.
So just ask him. Have an open conversation. It may not be what you think.