Sounds like you’re picking Phil over Beth. And I’m pretty sure if I were in Beth’s shoes that’s how it would feel. I probably wouldn’t want to have anything to do with you after that either.
Maybe find a way to talk to her that shows you’re putting her wishes above those of Phil.
Though i can understand why she is angry, i also see why it saddens you. I wouldnt push her too much, that might push her away even more? Perhaps just send 1 serious and kind written letter still, ask your pdoc or social worker to screen it first? Apologize sincerely and tell her you wont pressure her but you love her and your door is always open to her, no matter what? You cant force her into contact…
You are her mum, she might come back after things have cooled down? I know i was pissed at my mum for a while and now we are fine.
Oh and - dont stay with someone thinking you cant get better. You deserve better, surely.
Hope it works out well between you two. And that you find loving people around you. Feeling lonely or cut off from loved ones sucks. I also wish you wouldnt let phil hurt you. Be strong.