Hey Adam,
I might be wrong but here goes.
so you know you can hide buttons on mobile so they wont show up on desktop and viseversa right?
So all you have to do is have your desktop button going to an email form - might have to use mailchimp or similar to implement this
And on the mobile view - hide the button that takes you to the email form and create a new button that calls a number (right hand side you’ll see “go to URL” - under this dropdown menu there is ‘call a number’ )
Then back on your desktop view, hide your mobile button that calls a number
Hope this helps! 🙂
Yes, as @erayner pointed out, having two buttons and hiding the non-applicable one on desktop/mobile is the way to go.