you need to do this. 
Buy 5 ALNs (Additional local numbers… much cheaper then user licenses). These will be the new direct numbers for the deskphones. 
The 5 numbers which you currently have will be reassigned to Auto-receptionist. 
OPTIONAL: Give the numbers a name (for example the area they belong to) - this will appear when you receive a call so you know which number was being dialed.

Here is a step-by-step:

Buying 5 ALNs:
Phone System > Phone numbers > Number Inventory > Reserve numbers

Swapping the current direct numbers with the newly bought ALNs.
Phone System > Phones & Devices > User Phones > click on a device > Edit number > Select one of the newly bought ALNs.
When asked what to do with the old number - keep it in inventory.
Do this for all devices.

Once this is done you should have some random numbers as direct numbers for your phones, and your published company numbers which customers know should be sitting in inventory.

Next step 
Phone System > Phone numbers > All numbers > click on the numbers in inventory and assign them to Auto-Receptionist 
This means that they will ring the same extension as the main-number, i.e. they will ring the call queue and all phones.

Optional steps:
Phone System > phone numbers > all numbers > click on a number > give it a name
Phone System > Phone numbers > Groups > Call queues > click on a call queue > Call handling & Members > Display settings  » change it from Queue name + Caller ID name to Phone number name + Caller ID name.

The optional steps will make it so that when you receive a call on your display you’ll see the name of the phone number + the caller id of the person calling you.
 

How much does it cost for 1 ALN?

just go through the steps of purchasing a number - you’ll see how much it costs and you can confirm or cancel the order. In the UK it is £2 per number.