Remove Beta profile option on my iPhone

The support article you came here from should provide you with that answer. I'm assuming that you have installed the public beta of iOS 15 on your iPhone ... correct? If so, you should see the profile removal option. If not, as per your post, something else may have gone awry. In that case, you have two options:

1. Stop updating with newer beta release, and wait until an official release is provided by Apple.
2. Restore your phone using a previous backup BEFORE you installed the beta.

Once the beta profile is removed per the following, restore the iPhone > How to uninstall iOS beta software - Apple Support

If the beta was installed as part of the Apple beta test program, the option will be there. If the beta was installed from some website, possibly not. If the latter is the case, you will need to contact that website for assistance.

As of 08/27/2021 to remove Beta profile go to Settings -> General -> "VPN & Device Management"