Hello!

I moved from an iPhone 5S to my current 6S+ a year or so ago. I bought a few 6S+s that were broken and put together a Frankenstein working phone, which is now technically worth more than what I paid for parts, incl depreciation. I was wondering if I was to sell this phone, would I have to declare the money I would make from selling it? I've had a poke around this income tax calculator ( income-tax.co.uk ) which says I'd pay about £70-90 tax on the sale. Is this so? I'm not totally sure how it works and could use some advice. I want to put the money I get from it straight towards an iPhone X

Many thanks!