Don't take the risk with the one you link to but the other as linked to by ukhardy07 - here will be ideal.
It may be RJ11 at both end but the critical part is Cat5e (and only the thinner 2 pair which is good). RJ11 will fit into an RJ45 - they were designed to do that, or contact the seller and ask if he will make an RJ11 to RJ45 one for you and at your required length.. All his cables are hand made in the UK
He also, for example does RJ11 to RJ45 in Cat6 LINK
And this is the one you may need:
https://www.ebay.co.uk/itm/BT-Infinity-5M-Cat-5e-Mod... And at £9.99 cheaper than the link you have.
M H C
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