Hi NorthStarGuide and

You're not alone in coping with a partner with substance use issues plus BPD; that's no walk in the park. It is good to hear that he is trying sobriety?
Just to get a bit more background on your situation, how long have the two of you been together? Do you have any kids? And what catalyzed his decision to stop drinking?
In terms of your question here:
Would love to know your go to phrases when your loved one enters their borderline zone.
it might depend on what your goals are. If your goal is to protect yourself from hurtful words and actions, then in a sense, no words are required -- you're allowed to have
true boundaries and exit the situation.
If he is in a place where he isn't being hurtful, and you want to connect with him, then
true emotional validation may be the way to go.
Want to walk us through an example situation, and we can give you some ideas?
...
I am grieving what feels like the loss of my marriage, the loss of my person..... I'm thankful to find this community of support because to the outside world, my spouse is "normal", but to those of us who are close to him, we experience the chaos.
I'm starting to think that is a key step in choosing to stay in a relationship with a pwBPD -- grieving what you wanted and what could have been, and moving towards acceptance that this person is who he is.
As you process so much, do you have a therapist or counselor for yourself?
Looking forward to hearing more from you;
kells76