Carphone Warehouse is to close all its 531 standalone stores from April, resulting in 2,900 redundancies.
The firm says the move is not related to the coronavirus outbreak, but was because of changing mobile market.
There are Carphone Warehouse shops inside 305 big PC World and Curry’s stores, and these will be not affected by the changes.
Almost 40% of staff affected by the closures are expected to take new roles in the business, the firm said.
Group chief executive Alex Baldock said customers were increasingly buying online and from its big stores which sold computers and TVs as well as mobiles.
“They can’t find all this in the small mobile-only stores that are one twentieth of the size; they’re visiting these less and these stores are losing more money as a result,” he added.