Only my iPhone has slow wifi

I didn’t ask if there was anything new. I asked if any add-on security, add-on anti-malware, add-on VPN or other similar apps were installed. If you have any of those and whether installed yesterday or months ago, please remove them per the vendors’ instructions, restart, and test again.

Also check the Wi-Fi router firmware, and ensure it is current.

Failing that, restart both the iPhone and the router.

Any installed add-on security or privacy or content-filtering apps, or any installed VPN apps? If so, remove all of those, restart, and try again.