Using Microsoft Edge version 44.18305.1000, the LastPass,com Account Settings --> Phone Number (for SMS account recovery) page, i.e. https://lastpass.com/update_phonw.php
"add number" button does not work. This setting also does not appear in LastPass for iOS, or lastpass.com for mobile browsers like Safari and Firefox. I had to fire up ancient Internet Explorer to change my account recovery phone number. I guess I should be glad it doesn't require Netscape.