Support UI auth on adding phone numbers

src/i18n/strings/en_EN.json

@@ -3,6 +3,7 @@
     "This phone number is already in use": "This phone number is already in use",
     "Add Email Address": "Add Email Address",
     "Failed to verify email address: make sure you clicked the link in the email": "Failed to verify email address: make sure you clicked the link in the email",
+    "Add Phone Number": "Add Phone Number",
     "The platform you're on": "The platform you're on",
     "The version of Riot.im": "The version of Riot.im",
     "Whether or not you're logged in (we don't record your username)": "Whether or not you're logged in (we don't record your username)",