Someone do some calculations for me?

If I get £4 every week, how long would it take me to buy a IPhone 6 ( a cheap one)?

Brand new unlocked iPhone costs about US $ 750-850.
Conversion for that is to UK £ 550.

It will take you 137 days to save enough money to buy an iPhone if you save 4 UK pounds a week.

Almost three years if it's new and unlocked. Possibly far less if you buy one with a telephone subscription.