How to transfer contacts from flip phone to Iphone 8?

If the contacts from the flip phone are on the SIM for the flip, you would be able to import them to the iPhone, if the SIM from the flip fits into the iPhone. If not, then check with your carrier, many of them have software and devices that would read the old flip SIM, or the phone itself to transfer this content.

Sorry that it took that, but it is a prime example of moving from low to high tech. Shame to hear that about Verizon. I wonder how many other carrier representatives no longer are prepared to support those kinds of changes. I don't believe it is safe yet to believe everyone is using a smartphone.

If you are manually entering them into the iPhone, I suggest that you use iCloud, or another cloud service to manage the contacts, which then allows you to handle changes via the computer. A much larger screen and keyboard to work with, and then moving from one device to another is seamless. Besides iCloud, one can use contacts from your Gmail or many other email services. That may be something you can look into.