How to setup a phone for child (with parental control) with no other apple devices

To properly setup and manage any apple device for a child …

… the adult (the Family Organizer) needs their own apple device. (Apple’s term for this is a Trusted Device)

Create an Apple Account for your child - Apple Support

Use parental controls to manage your child's iPhone or iPad - Apple Support

That is correct.

You can’t even create a child’s account w/o your own Trusted Device.

The only cited “child account creation” options are “On your iPhone or iPad” or “On your Mac.”

(see 1st linked article in earlier reply)

You may be able to set up some Screen Time controls on your child's phone, and lock them by setting a Screen Time passcode on that phone, one that your child does not know.

Use Screen Time on your iPhone and iPad - Apple Support

However, I do not know if this will give you access to the full range of parental controls that are available if you are using Family Sharing. And if you're not using Family Sharing, you will need to have physical possession of your child's unlocked phone in order to set up the Screen Time controls. You cannot do this online.

FYI: Purchases directly from Apple generally include a “Return for full refund” for 14 days after receipt.

Returns & Refunds - Shopping Help - Apple

Except they’ll have to start-out by lying about the child’s age. (Because it can’t be a “child” account)

Circumventing established rules isn’t exactly teaching the best lesson in responsible internet usage. (Not to mention being a violation of the ToS)