Text message forwarding from one IPHONE to another

See this support document, How to forward SMS/MMS text messages from your iPhone to your iPad, iPod touch or Mac - Apple Support There is a * that tells you what to do if you do not see the Text Message Forwarding setting. Also, both devices must be signed into the same Apple ID.

I don't believe you can forward messages from one phone to another, only to your iPad, iPod or Mac.

If both phones are signed into the same Apple ID, you'll see the same iMessages on both. But each phone will only see the SMS messages sent to the mobile number assigned to that phone.