How do I remove Activation Lock on iPhone 14 Plus purchased from eBay?

Nope, the phone is useless if the original owner has not removed the Activation Lock themselves. Apple will not help and they do not get involved in any third party sales, so an eBay receipt is useless. If the seller is unable to remove the Activation Lock, then it could be a stolen device, otherwise they would have no problem doing it themselves.

A critical “proving” test is when the phone is initially powered-up it should display the script “Hello” before displaying language selection options.

You do NOT want a phone which doesn’t behave in this manner.

Unfortunately, this will probably not detect a phone carrier-locked to a carrier other than your own.

See also:

The All Too Common SAD Reality of Buying … - Apple Community

You do not remove Activation Lock on a used phone purchased from eBay.

A receipt for a second-hand sale is meaningless, and Apple will not remove Activation Lock on the phone, whether you submit the request online, or take the phone to an Apple Store. (Apple Store employees probably do not have the authority or the ability to remove Activation Lock, even if you were the original purchaser and had the required proof of original purchase.)

See: The All Too Common SAD Reality of Buying a Used iPad/iPhone – Apple Community

Unfortunately the iPhone cannot be bypassed by Activation Lock unless the owner puts in its original Apple Account and Password