It depends on what you think about using the extra verification for. I worked in the banking sector, and there it make complete sense to add phone number verification for 2 reasons.
1, it is more secure and the users data is safer this way.
2, the psychological factor. The user will feel safer using 2-step verification when handling sensitive information and might tend to using your website over one that doesn't have 2 step.
So analyse what market you will be designing for and then asses this information with the extra effort of 2step verification. In general I would go away from extra verification as it's quite a bit of extra work and users don't like the extra work. Keep it simple is my motto.
But on the other hand for marketing purposes you will have a contact number, which could also come in handy incase you need to contact the customer urgently.
Having a user login only with 2step verification is a valid option, but I would only recommend using it if this level of security is required.