List of users without Mobile device

I would like to export a list of users that have no mobile device associate in Exchange online.

using Powershell

Get-MobileDevice | export-csv test.csv

I am able to get a list of everyone who HAS a mobile device, but I would like the opposite effect.  We have  a company policy that requires email synced to mobile and this info will hep me perform an audit of employees.

Thanks!