Can I write that I had a phobia in my personal statement?
It is a judgement call. On the one hand, if you are sure it is no longer relevant, then mentioning it could be a problem since some would doubt you are cured, I think.
On the other hand, it shows personal growth. Congratulations.
But having grown as a person may not be as relevant to future research as you think. At least in the minds of others.
On balance, it seems best to not discuss it in written materials. If it comes up in an interview, it is again a judgement call whether it is wise to mention it. But, at that point, you will have more information on which to make the judgement.