This caused me a problem because I signed up with my personal email address, and then wanted a separate account for work but I only have one phone number and they won't let me use the same one on two accounts. I don't really care about giving them my phone number (it's out there everywhere anyway) but this has really reduced my ability to use their product.
Is this for the paid version? I'm using the free version, and it hasn't asked me for a phone number, but if the paid version requires a phone number, my reaction would be the same as yours: sorry, no.
In the age of eSIM, just order a free eSIM with zero credit, never charge it, never have any cost, and only enable it on your phone when a service like Anthropocene wants to send you some (completely unsecured) SMS code.
I would love to try their services, but they refuse to take my money.