Using two different browsers both with a VPN, I swapped my mobile phone numbers that had been verified. I could change the number to any number that had been verified, but could not change the number to an unverified number with out doing a verification.
I deleted history as i close Brave, opened Chromium logged in, was able to change verified numbers but not edit to a new number with out verification.
This leads me to believe that Ebay stores your verified mobile phone number.
It would not be the first service that would do this. You will find many services that once you give them information, they keep it until (by law) they can’t keep it anymore - even if you ‘remove’ it.
You will also find that, for example, Stripe will store any information that is entered into a field before you press submit/confirm. This is why it is very important to be aware of all data you give to the company before you press submit.
I try to delete all my information when closing an account. I edit any required fields with false information.
With ebay I decided to request all my data like a google take out.
I removed my PayPal account and all payment options. I plan to finish up by changing my phone number so I need a one time phone number.
I used to use mySudo for a burner number, are TextNow. I may wait until mid January and burn my Mint Mobile eSIM. IronVest charges me $7 for a masked phone number change, which I plan to do as needed but not real soon.