Hello abbyoiPhone,
Thanks for reaching out to the Apple Support Communities. I understand you've had some trouble with a phantom text message, and I have some information that may help.
Just to put your mind at ease, it's very difficult to track or monitor your iPhone without installing custom software to do so, which would require having physical access to your iPhone. It is, however, possible to remove that message. From here I'd recommend deleting the message, force closing the app, and then restarting your iPhone. Have a look at the articles below to learn how.
Use Messages on your iPhone, iPad, or iPod touch - Apple Support
When you delete a message or conversation, you can't get it back. So make sure that you save important information from your messages.
To delete a message:
- In a message conversation, touch and hold the message bubble that you want to delete, then tap More.
- Tap , then tap Delete Message. If you want to delete all messages in the thread, tap Delete All in the upper-left corner. Then tap Delete Conversation.
To delete a single conversation, swipe left over the conversation that you want to delete, tap Delete, then tap Delete again to confirm. To delete more than one conversation, open Messages and tap Edit in the upper-left corner. Then tap the circle next to the conversations and tap Delete in the bottom-right corner.
To keep your messages for a certain amount of time, go to Settings > Messages > Keep Messages. Then select how long you want to keep your messages.
How to force an app to close on your iPhone, iPad, or iPod touch - Apple Support
Restart your iPhone, iPad, or iPod touch - Apple Support
If the behavior persists or you run into any trouble, please reach out again.
Best Regards.