S.C.
Hi K.,
We had the same problem. My husband started to take him into the public potty and would let him stand on the seat to pee. It made him feel like a "Big boy" because now he can pee like Daddy, standing up. This got him over his fear totally and now he will also sit on a public potty (if we hold on to his hands). Before my husband did this, my son would not go to the potty in public with me.
The only other problem is the self-flushing toilets. Cover up the sensors on those.
Good luck!
S.