I need to see the text messages on this phone

I will need to make some assumptions since your post is not detailed. I am assuming that you do not have the iPhone in your possession OR you are unable to access the Messages section on your iPhone due to lack of passcode or Apple ID information. In this case you will need to see your carrier for help to see if they can send you a log of SMS texts.

If you have your iPhone in your possession then you can retrieve your texts from the backup that you may have created on your computer. Here is how to restore your iPhone from a computer bac up Restore your iPhone, iPad, or iPod touch from a backup - Apple Support NOTE that your text messages will only be restored up to the day and time your backup was created.

Axel F.

What happened to them?

Do you have a backup of the phone that was made when they were still there?

Have you turned on messages in the cloud?