Having a valid and verified phone number from all your guests is very important.

Requiring a phone number is probably something you want to have for all your guests, irrespective of the listing they select.

On the Custom Codes tab, select All listings to make your custom codes available without restriction to a particular listing.

You can just create your custom code (for example %%no_phone%%) with your own message, such as "Please do not forget to add your phone number to your Airbnb profile, it you be very appreciated in case of an emergency.".

Then, set the condition to "The guest has no phone number". Only users who have not verified their phone number with Airbnb will see this message.

You will only have to include the short codes %%no_phone%% in the templates you want.

Some booking platforms may not like hosts asking their guests for their phone numbers, if the platform doesn't already provide that information.

This may be because the platform prefers the host and guest to keep their communication on the booking platform's own communication channel.

Be mindful of these limitations and contact your booking platform for further instructions, if you have any doubts.