I personally believe verbal and quick moment of the phone won’t be needed. I could be completely wrong, or it might be an option as at+ is in pokemon go. But consider this, like pokemon go and ingress the best places to play will be metropolitan areas. Now picture people waving their phones around and saying/yelling (if your phones being waved around in a busy place you will have to shout pretty loud for your phone to hear you) spells. It would quickly give the game a bad reputation and cause bans and other issues that may lead to lawsuits.
Now what I could see is like ingress glyphs. With glyphs, you must connect 11 dots in patterns to draw specific glyphs you have seen before. With the 11 dots in ingress, they have a combination of 100 glyphs. Scale that to harry potter and you could have 100 spells. Add more dots and the number shoots up fast.
I know in some articles Niantic has talked about wizards unite using sounds tho.
Now I could see wizards unite having an add on device, such as pokemon go has with the go plus, or let’s go Pokeball, that is a wand with a couple gyroscopes that would allow you to perform the spell. Which would be awesome.
Again this is all speculation so I could be way off.