Which iPhones are compatible with Stylus pen?

None. iPhone was never designed to work with Apple Pencil or any electronic stylus for that matter.

Not supported, manufactured or sold by Apple for any iPhone model, past or present. Would you care to enlighten us?

Yes they do they have stylus pens for iPhones

Apple doesn't have any stylus pencil for the iPhone so would you care to let us know what electronic stylus is available for the iPhone?