At a guess, the big brands:
produce a phone that costs about £300 to make
sell them for a nominal £1000 fo make people think they're worth a lot more
let strategically chosen outlets buy them for £600
those outlets can sell them for £700-£850 to make you think you're getting a bargain despite still making £100 or more on the sale
everybody's happy, despite the end user having to pay way over what the phone ought to be worth
But the smaller brands:
produce a phone that costs about £150 to make
sell them direct for about £250
they've still got to charge the outlets £200 to cover distribution costs and profit
the outlets can't add more than about £30 to compete with the direct sale price so they don't make much profit, or they maybe choose to sell them below cost as loss leaders.
All prices guestimated, but sufficient to demonstrate why you'll mostly find the big brands sold here.
The same applies to biscuits, where you'll see a pack of biscuits probably costlng less than 50p to make, but priced "normally" at £2.78 so that the store can reduce them to £1 on alternate months and will probably sell more of them in the cheap months than they would in a year if they were properly priced at 75p all year round.