It may be more of a vent, but I am at the end of what I can handle.
Hello and welcome to the family! I'm sorry we're meeting under these circumstances but I am glad that you finally got your first post out of the way. I was in a similar situation with my BPD daughter and I can understand how you're feeling- it's no fin.
A few questions so everyone here will have a more complete picture- your son doesn't live with you and he has his own phone. Does that mean he's over 18? Who does he live with? And does he work or go to school? Who's paying his bills?
I realize that the threat of suicide is real for BPDs. But you also have to understand that they get what they want through manipulation. Every time your son treats you poorly and you allow it, then it encourages him to treat you as bad or even worse the next time.
When my daughter threatened suicide, I would dial 9-1-1 and send an ambulance. After the 2nd time, she never tried to manipulate me with that again. Why? Because for that one specific thing, she learned that her words had consequences.
Likewise, if my kid needed financial help and she called ranting away, I would say no 100% of the time. Deep down I knew that I'd eventually help her out if I could, but before money would transfer she was going to treat her dad with love and respect. Was she still manipulating me? Of course, but at least she was playing by my rules and treating me fairly.
You absolutely must set these boundaries and if that means blocking his phone, that's a great place to start. If he's ugly, block the # for 24 hours. Make that a predictable pattern so he understands that his outbursts are not acceptable.
You simply can't continue taking abuse and hoping that he gets better...you taking his abuse is preventing him from even considering that he's the problem. You must put up firm boundaries for yourself that clearly shows him, when you do <x>, then I'm going to do <y> because of your choice.
A golden thing a therapist told me years ago that always stuck with me is that mental illness has absolutely nothing to do with being nice. Being nice or mean is a choice that everyone can make, even narcissists and sociopaths have been known to be very kind, pleasant neighbors. Your son is choosing to be mean...the mental illness has nothing to do with that.
I hope that helps and again, welcome to the family!