Definitely put a filter/tracker on the phone and any other device he has access to, and let your son know you're doing it. A 14 year-old doesn't need unlimited access to all the hardcore porn the internet has to offer. Like other have said, if he wants it he'll be able to get to it but he won't have unlimited access... sort of how we were with playboys as kids. You got to see it but you didn't have an endless supply of it.
Do a little research on porn. It's a huge problem for a lot of people. Having a bunch of counselors in the family I hear about it ruining marriages quite often.
I would have a talk with him, something along the lines of, "I know you're interested in seeing this kind of thing, and it's a good thing and a good sign that you're maturing but trust me when I tell you you'll be better off not putting these images in your mind. When you do finally get to have sex with a real woman you won't have a bunch of preconceived ideas that are unrealistic. It will help you have better more satisfying relationships in the future."
You know he will still probably look at some stuff but at least you have planted the seed that gorging himself on porn isn't healthy.