Determining mobile/ cell number from two dimensions

[mark_plummer-16]

i have two numeric dimensions - home phone and work phone.  I want to create a custom dimension “Cell phone” that extracts from either field the mobile or cell phone number.

so for example

Home Phone  may equal   94991234

Work Phone may equal 0400000000

so my custom dimension “Cell Phone” should equal  0400000000

Coming for oracle Bi this was a simple task using a cast function but how can i achieve this in Looker?

I dont want to use a table calculation and don't have access to lookML

thanks