According to the site's research, eight out of 10 people have more than one old phone and only a third of those that are discarded are recycled.
This equates to 1.5 million handsets, which contain hazardous chemicals such as lead, cadmium and mercury, finding their way to landfill sites rather than recycling centres.
Some have also pointed the finger at businesses that do not recycle old mobiles, despite usually replacing phones in bulk when business contracts are renewed across the organisation.
"People regularly upgrade their phones to the latest model even though their old handset may be in good working order," said James Parker, manager of mobiles and broadband at Moneysupermarket.com.
"It is this need for the latest gadget which has resulted in people accumulating so many spare phones, particularly the younger generation."
The study revealed that the average Briton has two old handsets, with 32 per cent planning to keep hold of their old handsets as a backup or to give to friends and family.
The average teenager now owns three mobiles, but only a fifth of those surveyed said they plan to recycle any of them.
One in six respondents claimed that they did not know how to recycle old mobile phones or did not even know they could, while one in 10 said that they would prefer to sell their old phones, yet the price paid for recycling old handsets can amount to just as much as selling them.
National Recycle Your Phone Week will run from 27 October until 2 November in partnership with love2recycle.com which will pay an average of £25 per recycled phone, up to £150 depending on the handset.
To mark the launch of the campaign Moneysupermarket.com commissioned a giant phone to be made out of old handsets, which now stands in Golden Square in central London.
"We hope National Recycle Your Phone Week will raise awareness and really encourage people to recycle old phones for the benefit of the environment as well as gaining a bit of extra cash," concluded Parker.
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