If your European friend tells you their phone number and you write it down on your refrigerator (or your public blog for that matter), the French government isn’t going to come fine you for violating GDPR.
Is that what it says, or are you just saying they're not likely to enforce it in that way, and now we have a rarely enforced law that everybody violates and therefore the government can use it as a pretext to undemocratically destroy anybody that government officials don't like?
Wait, so you're saying it allows anyone to store and publish the personal information of Europeans? Without doing anything like have some way for people to contact you and request what information you have on them?
Which would also likely be perfectly legal under GDPR, assuming the phone number was given freely to you, we can reasonably assume informed consent.
As it's really hard to use a phone number for anything else than phoning someone, we can also reasonably say that the data is only used under the originally stated purposes.
And then the phone number is not shared with the public, but stored at a secure location (fridge) having organizational (family rules) and technical (locked doors, windows) policies in place to secure the information.
Given the required security level for a __single__ phone number I would say this would be a reasonable level of caution.