I had to trawl through all the eBay FAQs and dreadful AI bot until I finally got the 'call me' option to speak to a human.

The CSR told me how to find the customer address without buying a label:

Go to: 'Get prepaid label'->click on the pencil icon on 'delivery details' to see the shipping address.

Then I asked her how to find the buyer's phone number. She said 'it's not needed'. I said 'it is, as every courier needs to know the phone number to send notifications'. I'm using Parcel2Go to pick a service. She replied that it was not possible to find the customer's phone number and I would have to send a message asking for it.

I'm not running a business, I just sell things I no longer need. I'm going to stop listing on eBay until this nonsense is resolved or some entrepreneur creates a company to compete with eBay. I just don't have the time for this hassle.