allowing apps on iPad but not iPhone

My son has an iPad, and now we've gotten him an iPhone SE as his first phone. We've got all the Parental Controls working - for the most part.

I can see how I can hide/turn off some core Apple apps on his iPhone that I don't want him to have access to (such as Safari/Mail), but still keep them on his iPad. But I can't see how do that for 3rd party apps. For example we might be OK with him having Youtube on his iPad (since he watches that at home in a mostly controlled environment), but I might not want him to be able to access Youtube on his iPhone since he can take that anywhere.

Thanks!