How to let someone in with your phone?

There are two options for you when taking an Intercom call. You can make those changes by clicking on the Profile icon and selecting "Intercom Settings". 

You can utilize the Swiftlane app and you will be given the "Unlock Door" button to push to unlock the door for your visitor. 

If you are going to be taking intercom calls via a Regular Phone call then pushing 9 will unlock the door.