I don't know how young you are, or your husband, or how young these phone sex "girls" you are talking about, but if they are underage, counseling should be mandatory. I too don't know what the laws are as far as this type of behavior if they are under age, but if they are, your husband may very well have more problems than just the desire to talk.
I am going to assume that these "girls" are women, just younger women. You need to decide what you are wanting done in this situation. Are you wanting a divorce if he doesn't stop? Are you wanting to attempt to work things out if he is not willing to go to counseling? These are things you need to stop and think about, and decide where you want your life to go. You need to be asking yourself, and then have a talk with him and attempt to find the answers to what makes him do this instead of attempting to focus on your marriage? I am certainly not placing any blame on you, but you need to ask if either have become complacent in the marriage from the doldrums that happen sometimes in a marriage? Are both of you expending the kind of energy that it takes to keep the interest alive in a marriage?
If you are wanting a divorce, you need to seek counsel of a lawyer, and see where you stand from a legal stand point, before going any further. After that, you will have ammunition to talk to him about, and let him know that if his behavior doesn't change, this is what you are going to do, no more discussion about it.
I know you feel unappreciated, and unwanted at this point, but realize this is your husband's decision, and he would probably be doing this no matter who he was with. Communications is the cornerstone of any relationship, and you need to find a way, which therapy is one way to do this, to open up the communications between you and your husband, and both need to be honest with each other as to what happened to the excitement that has wained in your relationship.
Both of you, talking together, need to think of ways to bring the excitement back in your marriage, and to rekindle the fires that were there at the beginning. All of this will be difficult if he is not going to be a willing participant. If he is not, well you are back at the point of knowing what you do want. Are you willing to put up with this behavior?
If he is not willing to open up and get to the bottom of this, and you are not willing to put up with this behavior, then you are at an impasse, and need to think about turning to the future without him. You could be unwanted by him, but that does not mean you could not make a new start, and find someone who would want/appreciate you.
I hope this helps. Good luck.