@iiui awan
You must migrate them into t_item_epsilon table. If you used theme like gamma before, you can simply remove t_item_epsilon table and rename t_item_gamma to t_item_epsilon (this is valid for all themes those using t_item_{themename} table)
Sorry, this is true just in case you are using older Osclass version.
For Osclass that already have phone number on item, ideal is to migrate data into t_item table.
Just thinking about update statement to be made, for simplicity let's consider you were using veronika theme before and this theme is storing phone numbers in t_item_veronika table under column s_phone.
Following SQL should migrated data into t_item. Considering database prefix is oc_ by default.
UPDATE oc_t_item as i
INNER JOIN oc_t_item_veronika as v
ON i.pk_i_id = v.fk_i_item_id
SET i.s_contact_phone = v.s_phone
WHERE coalesce(v.s_phone, '') <> ''
If you still not sure what to do, hire developer.