Hello Ash-2631,
I believe you are referencing the arrow-turning-underneath-text glyph icon? If so, this is a message summarization feature of Apple Intelligence. Basically, your phone uses AI to summarize the latest message in the specific conversation. You can always disable this if you so desire:
Summarize notifications and reduce interruptions with Apple Intelligence on iPhone - Apple Support
- Go to Settings on your iPhone
- Select Notifications -> Summarize Notifications
- You can now turn off Summarize Notifications
For more information on Apple Intelligence visit Apple Intelligence - Apple
If this symbol wasn't what you were referring to, just let me know and we'll go from there.
Have a nice evening.