If he's doing better and is stable on the dose given, I would NOT want to change anything...period!

I had a dog on pheno, once he was stabilized it was the greatest thing and I never wanted to go back to what was prior - major seizures, etc.

I understand Pheno is not the greatest drug to be on, and if this was a younger dog, I'd definitely tell you to slowly wean him off - if possible and look for alternatives; but on an older guy....no way would I change anything if he's back to himself!