But the donation link redirected me to PayPal where making a donation by credit card requires to enter phone number and email. Usually this is not required for credit card payments and I don't want to give my phone number to PayPal.
The donations are handled by the SFC on behalf of OpenWrt. If you look at their
page, you'll see this:
Donate to our projects
Finally, Conservancy also maintains directed donation programs for its member projects. Using the PayPal Donate button on that page is the easiest way to donate to a specific project. You can also designate a donation for a project in the memo line of a check or wire transfer.
So check or wire transfer are options. But maybe not credit card without PayPal.
I have the same experience, I have a paypal account with over $ 100 USD on it and wanted to donate from it but I could not as they wanted my credit card number etc.
I do not have one so cannot donate despite the more than $100 on my paypal account.