One of America's biggest law firms is set to launch an investigation into the conduct of former Phones 4U directors.Quinn Emanuel Urquhart and Sullivan was appointed last week by PricewaterhouseCoopers (PwC), the firm's administrator, and will examine the actions of EE and Vodafone which decided against renewing their deals with Phones 4U in the weeks preceding the company's collapse.Thousands of staff were left without a job as the phone retailer went into administration in September and the company's former bosses could face legal action if the law firm can build enough evidence for a legitimate claim against them for breaching their fiduciary duties, Sky News reported.After PwC's appointment, Vodafone, EE and Dixons Carphone reached agreements with the administrator to acquire various Phones 4U assets, managing to preserve over than 2,000 jobs, but several hundred shops were force to close and only about 520 staff continued to work at Phones4U in October on the wind-down of the firm's operations.