We are looking for the option to call out with our local company phone-number

Hi,

You don't write if you use Skype for Business Online or Skype for Busines On-Premises, but it is possible with both. You can set an policy with an fixed number that will be showed when you call out, but this policy will be active on all outgoing calls so you users will never show their own number. The other option is to create a new user and assign a policy to that user with the local company number, then set all users as delegates to this new user and they will have the option to place new calls as this user.

Create a new policy with Skype for Business Online. The articles below show how to connect with Powershell and create a new policy that will change the Caller ID for all users using this policy, note that it will be like this for all calls.

https://docs.microsoft.com/en-us/skypeforbusiness/what-are-calling-plans-in-office-365/set-the-caller-id-for-a-user

https://docs.microsoft.com/en-us/powershell/module/skype/new-cscallinglineidentity?view=skype-ps

With Skype for Business On-prem there is another policy you have to create and assign to your users. Create a new Voice policy or modify an existing one. Change the Alternate Caller ID value and set the company phone number that you would like so show.

https://docs.microsoft.com/en-us/skypeforbusiness/deploy/deploy-enterprise-voice/caller-id-presentation-rules

You could also setup an extra user and add the other users as delegate for this user. They will then be able to make a call as delegate.
https://support.office.com/en-us/article/act-as-a-delegate-or-delegator-in-skype-for-business-16bb9209-a0ab-4005-94b1-fb2e99c85e84