A long time ago they wanted a phone number for me to get a hair cut. She looked at me like I was crazy when I said no.

I do this all the time.

"Can I have your address?"

"For a haircut? No, will it let you skip it? Ok good do that then, thanks. I don't need 50 new mailers a month about damn haircuts, you feel me."

Problem solved.

I realized a few years ago that my GF inadvertently solved this issue for me: She likes registering for anything that provides a discount, so I use her phone number.

"Are you a member?"
"Nope, but my GF probably is..", and 90% of the time I am correct.

It’s been more than 20y since the first time I remember sternly declining to give either a phone number or postal code to a cashier in a retail shop. It pissed me off then and still pissed me off now.

Why don't you just lie ... Each time a different name surname email address physical address phone number ... Yeah sometimes it's Mandatory to use a real address for delivery purposes just put a random name in and add a post-it on the doorbell saing something on the line of leave packages for Crudelia demon here please. Temp mail for most discounts is enough... The test cases in which they do not only ask for your phone but also want to verify it it's pretty slim ...

Here it's similar. I've found out that if to the question

do you have our membership?

I respond "No, thank you", they often understand correctly and don't assume I want to set one up

I encountered this in a computer club (I mean the place where you play per hour to play computer games on a good PC if you lack a suitable one at home). The accounts there were using phone numbers as usernames, and apparently if one is used, it would have to be verified. However, after refusing I was just given one-time accounts every time (with a random string of digits as the username), I just couldn't save unspent time for another visit so had to pay precisely. Funnily enough, the host herself the first time mentioned one-time phone number rental services for this reason)