The first hing to do when getting a cellphone account is to find out which carrier(s) gives you good service in the places you need service. Evidently you didn't check Verizon service at work before you chose Verizon as your carrier.
There's no way to increase the signal (unless there's somewhere in the office, even near he ceiling, that has good service, and you get a nanocell, or you want to try one of Verizon's little gadgets that provides you with cellphone service over your internet connection.
Once your contract expires, find out which carrier provides service where you need it, then switch to them. (You'll have to buy a different phone, of course.)
But if you're looking for an app, or a cheap way of doing it, sorry, there is none.
