To make a default phone field a drop-down instead of number

Cx is using the sales dialer and has integrated his pipedrive account with the sales dialer. cx stated end users have two phone numbers associated with them. When the campaign gets created on Sales Dialer, it only gives the first number for that contact. We need to be able to call the second number, too, if the first number does not work. Have asked cx to create 2 different custom fields and map the details accurately as per the pipedrive. however, cx does not want to do that and wants to make the default phone field a drop-down instead of a number.