I usually buy second hand off members market but now I've just been buying brand new Chinese phones.
I too buy whatever phone I want. Me paying £300 in one go is easy when I'm saving £62 a month compared to you.
Current phone Poco f2 pro go check the specs on GSM arena. I've had it for a while now and I paid £300 for it a few weeks after it launched.
The phone before that iirc was a Sony. I bought second hand used it for a year and sold it on for what I paid for it so the phone cost me nothing.
I could sell my phone right now for £250-£260 on eBay. Therefore it's cost me £50 to own it for a year.
You are paying more than that per month.
https://www.google.com/amp/s/m.gsmarena.com/xiaomi_poco_f2_pro-ampp-10220.php
Here's the spec of my phone above just so you can understand that it's not crap in any way and I'm sure if you compare it directly with whatever it is you are using you would see what a terrible waste it is.
As for if you don't have £300 lump sum even using PayPal credit or a interest free credit card would work out cheaper especially if it saves you £60 a month.
There's a girl who I work with who spends £400 leasing an Audi and always has the latest iPhone for £80 a month, etc.
Guess what she's nearly 30 and lives at home and doesn't have any savings. She's going to find it hard whenever she finally moves out. She also has very high expectations of men she dates for them to throw money about like she does.
Problem is those men won't be living with mummy so they know the true value of money.
You are paying £840 a year for a phone. I've probably spent around that in a decade overall and I've always had a decent phone.