Klaviyo also provides SMS marketing which is a very powerful tool to have in certain industries. You could capture a phone number and subscribe it to Klaviyo for future marketing or automation flows.
You can subscribe a phone number to a different list from the one the rest of the form is linked to. Just select the phone field and select the list you want it mapped to.
Number Formatting
Klaviyo only accepts phone numbers in E.164 format – International phone format. Eg. +1234567890. You can read more here https://help.klaviyo.com/hc/en-us/articles/360046055671
You can enable the “Intl. Phone Formatting” feature in the additional form settings section to ensure phone numbers are collected in the correct format.
SMS List Setup
Your list must be setup to accept SMS subscription. You can find some information and instructions at Klaviyo here https://help.klaviyo.com/hc/en-us/articles/4404274419355
Here some more interesting information from Klaviyo about SMS Marketing https://help.klaviyo.com/hc/en-us/articles/360047879512