Oh dear. You fell for a woman out to squeeze all she could from you (admitted that yourself) and she walked off with a phone you willingly gave her and didn't return it when asked. Seriously, you thought she would after what you had been through while in the relationship?
I got angry with an ex a long time ago and felt so aggrieved I demanded a loan back. Never got it, and thank goodness I found a lawyer who told me I never would and to get on with life instead. He let me vent my anger in one legal letter and then turn away. Best $5k I ever spent.
Walk away, learn from the experience. Run if another of her type crosses your path, at least now you can see what lies ahead.
It's a phone, it's a 'thing'. Keep your dignity intact.
...and with a nod to @Markx for letting me know I had put this in the wrong thread