It's great that you're trying everything you can to help your son
through this. As an mom with a button phobia and a 7-year-old son, I
can understand both sides.

Switching to snaps may help, but it may not, as a certain amount of
disgust surrounds the whole idea of buttons even having been on the
shirt. Think about it like this--he feels the same way about buttons
that you probably feel about...cockroaches. They're nasty and you
don't want to think about any place you know they've been. However
unreasonable the phobia may be, to sufferers it feels as real as the
more common reaction to creepy crawly things. For this reason, I
don't think that either short bursts of exposure or positive
associations will help. I'm sure all the positive experiences I've
had in my life have taken place in proximity to buttons, but I don't
feel any less creeped out by the damn things.

Having said that, do as you're doing: offer some possible solutions,
but let him make the decision he feels comfortable with. He'll be
fine. Dozens of us in this group have made it all these years
without even knowing there was anyone else who shared our feelings.
Your son can now connect with others, and maybe as a group they'll
come up with some new uniform designs. Yeah!