Ideally you want to know the scope of the phone network but as your network admin is on leave it's time for some trial and error
1st IP 10.22.0.253 subnetmask 255.255.255.0
This will allow you to access the 10.22.0.* range
2nd IP 10.22.0.253 subnetmask 255.255.0.0
This will allow you to access the 10.22.*.* range
Test on both to see if you can reach or use a network scanner to see if they are visible
The big problem you will run into is your phone network and computer network will most likely operate on difference a VLAN so there might be no way of accessing them even though your on the same hardware
But don't assume a VLAN has been set up and try running on the above
Also this is a good solid guide to subnet masking but is written by Microsoft techs so reads like a black brick if you were interested but the best would be to take a class on networking and learn from real world application