Officiant!

You can ask him the way you want: a phone call or in-person.

However I wouldn't bring a 'proposal box' or a gift while you're 'asking'.

The only thing that matters is the fact you'll ask him formally and just for that. You'll make him happy.

We have the same situation. I just said, "consider this our official request that you be our officiant."

We have our 2 closest friends officiating, both of them absolutely knew and were on board to co-officiate for us!

One lives out of state from us so we sent her a box of cupcakes with the note "Will you co-officiate our wedding?" and Facetimed her.

The other lives down the street, and he came over one night and we sang "You've got a Friend in Me" but with a few lyrical changes, and the end being "So matt will you marry us?" rathers than "Boy you've got a friend in me" (Music is a huge part of that friendship haha)

Both are more than necessary, but we wanted to make it special!

"Hey are you available to officiate our wedding on dd/mm/yy?" lol no seriously though, don't skip a contract just cuz they are your friend. The last thing you want is to be screwed at crunch time.

Meet up with him for drinks or dinner and just ask him together.