Apple Pay on the Web requires my phone and email. Is that information shared? I chose Apple Pay while paying on a website using an iPad (iOS 13) and then a Mac OS (Mojave), and got a pop-up asking for my phone number and an email. The website I was on already has that information. The pop-up was legit from Apple Pay.

I was under impression Apple Pay won't ask for (and especially share) any information unless it's absolutely necessary. Apple Pay on my Mac never asked for any of this before. 

Is there any official source explaining why is that information required, and what information would be shared with the merchant? (I.e. will it maybe obfuscate my email like Apple Sign in would?)

I only found irrelevant articles on applying for the Apple Pay physical card, as well as this, but it doesn't answer.
Only being asked these details while on a Mac enabled me to use desktop Safari's Network Inspector, and actually see what's being sent to the server.

When prompted, I couldn't choose an existing contact, so I had to create a new one (but it wasn't added to my Contacts either, even though the payment went through). Lets say I used John Doe with +1 (505) 842-5662 and myemail@example.com.

The request was sent to https://ticket-shop.example.com/api/v3/payment/applepay/fast-checkout with the following data:

{
    "paymentData":{
        "paymentData":{
            "version":"EC_v1",
            "data":"SOME_BASE64_LOOKING_STRING",
            "signature":"SOME_BASE64_LOOKING_STRING",
            "header":{
                "ephemeralPublicKey":"SOME_BASE64_LOOKING_STRING",
                "transactionId":"SOME_HASH"
            }
        },
        "paymentMethod":{
            "displayName":"MasterCard 1234",
            "network":"MasterCard",
            "type":"debit"
        },
        "transactionIdentifier":"SOME_HASH"
    },
    "eventAlias":"example-standup",
    "consumerContact":{
        "emailAddress":"myemail@example.com",
        "familyName":"Doe",
        "givenName":"John",
        "phoneNumber":"+1 (505) 842-5662",
        "phoneticFamilyName":"",
        "phoneticGivenName":""
    },
    "_csrf-frontend":"SOME_BASE64_LOOKING_STRING"
}


So Apple Pay did share that information with the merchant. Moreover, in a confirmation e-mail I received from them, they used the test name I entered while paying, not the name they have on file for me. 

So apparently some merchants will request this additional info, while others don't. I couldn't find any official sources, so this is merely an observation that didn't fit into a comment, and not an answer.