Hi! That is hard! I guess it doesn't help for people to say "Oh, well, I didn't have that problem, my kids were easy!" BUT how can people advise you if they failed at potty training?! lol..anyway, without sounding preachy, I potty trained my first daughter for poo at 18 months and by 24 months she was dry all day and night...never had one accident since. My second daughter was 24 months as well, but had a more accidents, but by 2 years, 4 months she was dry all night and day...with an accident every couple of months or so.
So I tell you this, not to brag, but to help. To tell you what I did.
Starting at 14 months, I put my older daughter on the potty. Sometimes she would pee and I would clap. I would give her M&Ms and we would call Elmo on the phone. She went a week in undies at 18 months with no accidents, but I realized it was me who was trained..not her. I took her potty every 2 hours. I would let her watch TV if she sat on her potty while watching. She came to the potty with me everytime I went. She also went with Grandma and daddy. It wasn't always easy. At 19 months she stood in a display window at the GAP and peed. FUN! But poo was done at 18 months...this is how...
I never ever said the potty was gross...BUT I did say "yuck" when I changed her poo. Any time she had to poo, I could tell. I just knew. I don't know how. BUT I would put her on the potty and hold her until she poo'ed...that was that. eventually she told me. I never expected her to do it by herself. We always did it together. SO about 6 months later, she was completely potty trained.
I could have waited a year and did it in a weekend.
So I guess in your situation, with the phobia, I would put the potty chair in a happy place. Put her in a diaper. Let her sit on the chair to eat candy or watch TV...(My kids don't do much of these things now despite my using them to teach!)
When she is happy with sitting on the chair...like it is a chair, let her go naked for a few days...have her sit on the chair naked, but don't expect her to do anything in it. Let her have the candy.
When she is totally comfortable, ask her to tinkle...show her how if you have to. Reward her...clap...call friends...whatever..
Good luck...
I am certainly NO expert...so, take or leave the advise and VERY good luck to you!