Just Eat's normally relaxed chief executive David Buttress looks bothered. The 40-year-old boss of the online takeaway ordering service tells IBTimes UK: "Around 50% of people who order a takeaway in the UK use the phone. In some parts of the world this rises to 80% or 90%.

"In the markets we operate in, takeaway food is worth £24bn (31bn, €29bn) a year. If we can get more people to order online there is real growth here for us."

Buttress' battle with the telephone brings to mind Roberto Goizueta, who was chief executive of Coca-Cola for 17 years until 1997. He was once asked in the US giant's 1980s heyday whether its main rival was Pepsi. He replied: "The enemy is coffee, milk, tea and water."

Like Coke in the 1980s Buttress knows what it's like to lead the pack.

The takeaway service, launched in Denmark in 2001, is the market leader in all of the 15 countries it operates in except the Benelux nations.

In the UK, the firm's largest market, 27,000 restaurants are signed up to its service out of a national takeaway market of around 35,000. In total the group has operations in 64,000 takeaway restaurants in such countries as Italy, Mexico, Brazil and Canada.

Restaurants in the UK pay just under £700 to join the network as well as 13% of each online order.

Buttress was part of a team of two who set up the UK business in 2006. Eight years later the group floated in London with a £1.47bn valuation, the market price of the business has since doubled to £3.2bn. Last year sales jumped 58% to £247.6m, while pre-tax profit came in at £34.6m.

With such large market shares the way Buttress plans to expand the business is by boosting orders rather than signing up more restaurants, which has been an engine of growth in the past.

"We run a world class platform," says Buttress. "We offer tracking and notifications, so a customer knows their food is on its way."

"We have literally millions of customer ratings of restaurants on our site. And that can help improve restaurants. An owner can see he may be the fourth best Pizza business in his area. And he will be able to tell whether its the quality of the food, or delivery times, or something else that is letting him down."

Some analysts warn that Just Eat's growth is set to slow due to increasing competition from rival Hungry House and higher end food service Deliveroo. It also faces a battle from newer rivals such as Uber and talk that online giant Amazon may also enter this market.

But Buttress says he does not lose any sleep over this. He says: "We have a phenomenal position in the UK and other markets. The group has long-standing restaurant relationships. There has been long been talk of rivals coming into this market. Competition is a normal thing."

Buttress also has no intention of using the online platform the firm has built to diversify into other areas in the way cab service Uber is developing driverless cars, or the path that has led online book service Amazon into everything from selling groceries to TV production.

He says: "We are a hybrid tech firm and a sales and marketing operation. But you won't see us going into a broad range of services. You lose discipline and focus. A lot of the great companies in the world do one or two things well, and constantly look to innovate in that area."

Buttress has come a long way since he met Just Eat's Danish co-founder Jesper Buch in 2006. At the time Buttress was head of Coke's restaurant business in the UK and Ireland. He joined the soft drinks group eight years before as a graduate trainee after completing a business and law degree at Middlesex University.

The pair struck up a friendship and after several months Buch convinced Buttress to help start the UK business along with one other early investor. "It was a strong idea", said Buttress. "And I did not understand why anybody had not thought of it before."

They started the UK business from a basement flat in Canary Wharf. Buttress spent months walking along Commercial Road and the streets of East London trying to get takeaway owners to sign up to something that at the time did not exist in the UK.

"I set myself a target that I would not go home unless I had signed at least one business that day," says Buttress.

But after a few years the business gathered a head of steam in the UK. Buch sold his stake during a 2011 fundraising and retired to Spain, where he funds various start up firms. His successor Klaus Nyengaard left as head of the online operation in 2013, which then saw Buttress handed the top job.

The married father-of-two says he often works late into evenings after putting his children to bed. No doubt thinking about how he can get hungry people to use the telephone less.