Most of the posts on here are absolutely rubbish; just ignore them, and listen to what I have to say. I've helped businesses in this situation before - here you go:
Your shop is not that big if you're only 6 servers, and you're only in the PRE-evacuation. You have time to do this right. Everything out of the datacenter but the wiring. Leave the racks too. The only thing you need is the physical equipment, your data, and a way for continuation after re-establishment somewhere else (Backups). Ensure you've grabbed all backup tapes that may be on-site. 6 servers will not take you that long to evacuate. Your datacenter is most likely a wiring closet or something equivalent, so take the extra time to label things. Make a diagram or map before you start removing things so you know how to put it back together. If you have some networking equipment scattered throughout the premises, ensure to grab that stuff too. Remember, you're not on fire yet. You have time to think this over and get all of the REALLY important stuff.
You have two options for how you want to handle the client workstations and IP phones. The first option is for you and your IT team to go around to each one with a cardboard box and pack it all up. The second option is to give each employee a cardboard box and have them pack their own workspace - why should you guys have to do everything? Unfortunately, NON-IT workstation users are stupid and do not always store company data on their assigned network storage, so your workstations are actually assets, that could be holding data that is not replaceable. Because you mentioned all of the items (servers, workstations, networking equip. and phones) in your post, I'm assuming skipping them is not an option. Go with the fastest - each employee packs their own workspace. Get support from management to make it happen, it would save you and your team time as well as expedite the evacuation process. Each employee packing their own workspace also ensures they grab the things that are necessary that may be hiding in their desks/around their workspace.
The rest is up to you. Really, and I know you've probably heard this 100x and read about it several times from the comments above - but the organization is not taking itself seriously if it does not have any type of protection from this type of disaster/condition. I don't have to spell out the obvious, but if the organization exists in an area that is prone for this type of disaster, then the business should have been designed to "hit the road" in the event this type of condition threatened the business... as well as protection and correction.
