American buyout giant Providence Equity is understood to be reviewing options for the company, which it bought from founder John Caudwell in 2006.
Trade rivals keen to expand their presence are thought to be the likeliest interested parties as Phones 4 U operates 476 stores across the UK. Dixons is a possible suitor.
A sale would result in a second windfall for Caudwell. He kept a small stake in the business after raking in £1.5bn from selling his empire four years ago, which included other operations such as distributor 20:20.
Analysts estimate the business to be currently worth between £700 and £800m.
The group began in 1987 when Caudwell bought 26 phones from the US for more than £1,000 each and sold them on in the UK.
At the start it took him eight months to sell all of the phones, but by the time he sold Phones4U it was selling 26 mobiles a minute.