If you hire contractors to staff a phone bank, the contractors don't get to bring in their own phones to use, you can make them use your own phone system.
And if you hire a 3rd party corporation to do that, you're in the clear. Of course those people are often W2 employees of that corporation.
If you bring in a bunch of individuals and tell them what to do, how to do it, and even when to do it (Uber, for example, doesn't compensate you the same way if you won't work during their required hours) then that starts to look a whole lot like you have employees and are trying to dodge the tax consequences thereof.
As a tech contractor myself, I won't sub out to anyone who doesn't have an LLC and always represented myself behind one for the good of my clients.