The savagery

I would think it would be pretty legal. And it's not doxxing, doxxing is intentionally putting out someone's personal info out there, usually with intentions to have people harass or harm the individual. BUT if something were to happen with the ex in this situation I think there could be legal action as they put them in the situation.

There is no lawsuit for giving out a phone number unless you had an actual agreement with the person about keeping it confidential. If you did have such an agreement, it is possible that you might be able to sue for breach of contract. However you would need to have suffered some tangible injury. Something a court could redress. So, I’m pretty confident in saying there is nothing to sue for.

Well I mean in a case where someone was harassing or stalked the owner of the phone number or if some physical harm came from that you could probably sue for negligence or endangerment? Or maybe as a more likely case the owner of the number can sue for the cost of having their number changed if they keep getting unwarranted calls and texts ?

Well, those would most likely be considered tangible injury. A court could provide a remedy for that. So yeah, in that case you could probably have a lawsuit.