A lot of phones nowadays are glued shut, you'll budget for a trained repair tech to do that. They also use the battery as a giant capacitor to absorb spike draws that wall chargers cannot provide, so the modified device will need that capacity as well. Finally, there will be some radio certification ambiguity as to whether it's legal for a legal company to operate.

That said... there are Chinese rackable phone KVM thing, available on Chinese e-commerce sites, intended for social media fraud farms(faking likes, aiding account thefts, sending scam DMs, calls, SMS, etc). Taking them apart should be already common in those scenes. Reportedly those are operating at some scales globally in various third world scam malls - shopping malls by architecture, but operated by gangs and inhabited by scam shops. So it's readily possible, if necessary.