How can I set up parental controls on iPhone?

You can start here where there is a list of specific controls that you can use.

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

Some fundamentals up front.

1) An “Apple Family” needs to be established if one does not already exist:

Set up Family Sharing - Apple Support

2) Next, the Family Organizer needs to create the child’s Apple Account from the Organizer’s device.

Ensure that the child’s birthdate is accurately entered; attempting to change it later is problematic.

Create an Apple Account for your child - Apple Support

3) Next, the adult needs to setup the child’s device, being careful to choose the “setup device for a child” option.

4) Then, “lockdown” the child’s account w/ the info at the link Mac Jim ID provided

Don’t let the child know what your “secret” Screen Time passcode is on their device. (compromise of this passcode allows them to “be you.”)

Uding the Screen Time controls is not all that straightforward at first. Invest some “quality time” in it’s setup and TEST your settings.

Finally, highly recommend that you lock-down “Account Changes” to prevent your child from making those changes w/o your knowledge.

Best of luck.