The template for bookings is in wp-content/plugins/events-manager/templates/placeholders/bookingform.php
If you want to modify bookingform.php you can copy it to wp-content/plugin-templates/events-manager/templates/placeholders and then make your modifications. You could even create custom fields if you know how.
The template for the booking fields (including the telephone number) is here: wp-content/plugins/events-manager/templates/forms/bookingform/booking-fields.php
If you want to modify booking-fields.php you can copy it to wp-content/plugin-templates/events-manager/templates/forms/bookingform and then make your modifications.
