This may sound trite, but it's true. If you don't look around for whatever product or service you need, you probably won't get the best deal. How likely is it that the first quote you get will be the best option?
Notice I didn't say the lowest cost. Low cost is not always the best choice.
This is particularly true when dealing with an incumbent. Your current landlord is an incumbent. The landlord knows that it's far easier for tenant to simply renew its lease than move. Moving costs are avoided. Production doesn't go down due to the disruption of a move. So the incumbent landlord usually quotes a rental rate that is higher than what they might give a new tenant.
So when your office lease renews, shop the market for other options even if you really want to stay where you are. This gives you other points of reference. It also tells your incumbent landlord that you have other options and are willing to leave if you find a better deal.
The other recommendation is that you hire a Corporate Real Estate Advisor or Tenant Rep. This will sound self-serving since I am one of those, but when I was a landlord I found that the building owner usually got a 10-20% better deal if the renewing tenant didn't have a broker. The landlord assumes that the tenant isn't shopping the market if they don't hire a broker. Since the broker doesn't cost the tenant anything, there is no downside to having representation.
So shop. For space. For phones. For movers. For contractors. And enjoy the savings or at least the confidence that you got a good deal.