According to Media Week, the company has signed a six-figure deal which will see its branding accompanying the show's transmissions on Channel 4, E4 and video on-demand, as well as those of spinoff Hollyoaks Later.
It is understood that the contract will run for three months and take effect from October 1.
Caspar Nelson, Phones4U's head of brand communications, commented: "Our research has shown that Hollyoaks is the most-watched TV show by our core customers, who can relate to its youth-orientated storylines.
"We're chuffed to be sponsoring such a popular drama that, like our brand, is not afraid to be edgy and irreverent in the way it engages its audience."
Hollyoaks' current sponsor is camera manufacturer Nikon, which has been using the teen programme to promote its Coolpix S3000 product in a five-month deal. The show was previously sponsored by chewing gum brand Wrigley's Extra between 2005 and 2009.