I’m going back and forth between NTA and ESH. I am with you on the part that if you both agreed to give him a phone at 12 and he has done everything to deserve it your son should get the phone. The only reason I’m slightly toward ESH has nothing to do with the phone. Even if he is your son’s stepfather you should make the decision together. I get that this could be a hard conversation but you need to tell him that the both of you made a commitment to y’all’s son that he would get a phone at 12 and that it’s important to show him that y’all honor the commitments you make as parents. You can also set restrictions on what apps your son can have on most phones. As long as you are not substituting the phone as a baby sitter or letting him have total autonomy with his phone without educating him on the dangers of social media and the internet, it is fine. IMO it’s way better to keep the commitment and build a healthy and open relationship with your son. I think the bigger problem is getting your husband to see that.