If you store phone numbers in phone_id and you need to populate the phone attribute using value from phone_id you can setup simple scenario use case with repeat daily trigger (or NOW/SCHEDULE trigger).
However, the above will only work when phone_id contains only 1 value - is a string. If on other hand your phone_id contains multiple values - is list of strings - you can utilize the code below and insert it in the set attribute node.
{% if customer_ids.phone_id is string %}
{{customer_ids.phone_id}}
{% elif customer_ids.phone_id is iterable and customer_ids.phone_id | length > 1 %}
{{customer_ids.phone_id |last}}
{% endif %}
The code above checks if the phone_id is a string, if yes it will insert the single value that is there. However, if its list of strings it will populate the phone with last value from the list stored in the phone_id
Always TEST the implementation above on testing customer profile to verify if all works as expected before applying LIVE.