While this is possible, it's not something we recommend if maximum number of leads if your goal. Based on testing, requiring a lead to enter their phone number can not only significantly reduce the number of leads you receive but also your cost per lead.
Ultimately, when someone clicks on your ad, they are looking to be able to view homes. Immediately requiring an email and phone number will push some people away.
For example, would you ever go to a car dealership that required your social security number to even browse what cars they had? Probably not. The ones that do provide that information are probably more serious but how many people do you push away in the short term by doing this?
Lastly, when requiring a phone number, you leave yourself open to people providing fake information just to get past the registration.