As verification and personalization is making its way into everyday apps and services, users are expected to provide and verify their email and phone number.
I have noticed the following is a common way to do this verification,
Total number of interactions (taps) required: 5 or 7
The following is one of the alternatives, that worked well for me during user testing.
Total number of interactions: 2
The only issue is when the user is on a tablet device when registering, as most tablets are not capable of placing phone calls. Other than that, there are no realistic issues with this workflow. It is highly efficient and keeps the user engaged with in the app.