My horse was like this when I first got her. She always bolts if she is facing one way (facing the rest of the horses outside) so I turn her around so har butt is near the other horses and her face is looking out the screen door so she can look at birds/cats/field. Not sure if you can do this but that really helped for my mare. Then I slowly started to build up her tolerance. I would bring her in and as soon as she got antsy i would lead her outside before she could bolt. I would do this to show her that everyone is still outside and safe, and then I would bring her back in. For the first few times on the cross ties try not brushing or tacking up, just have treats to keep him distracted and then after a few minutes lead him out and he will realize that nothing happened while he was in there.
My pony used to break the crossties constantly, so what I did was always talk to her in the crossties, and make sure she had something to keep her mind busy so she wouldn’t run out. It is hard and took a very long time, and now she is only scared of one crosstie stall in particular. Another thing I did was have her stand in the tack up stall with out putting on the crosstie and just have her stand there for a minute, then reward her, then put on one crosstie for a little bit, then reward her if she did good, and finally put on the last crosstie for a longer time than the other 2 and reward her lots.