By default, when you send an email from your iPhone, a “Sent from my iPhone” signature will be added to your message. You can edit this following these steps:
Step 1: From your iPhone home screen go to the Settings menu.
Step 2: Tap on the Mail icon.
Step 3: Select Signature.
Step 4: There, you can modify the signature for all mail accounts you have set up. If you wish to have no signature, simply delete the entire text.
Step 5: When ready, tap Mail on the upper left corner to save your changes