Another solution is to ensure your router or switch is not prioritizing traffic such as with QOS. Many consumers are now purchasing professional grade routers which often have QOS-like features enabled by default resulting in deprioritized speed to devices like iPhones.
A prime example which is becoming more common in product complaints is seen with devices like the Edgerouter series. Very strong pro-sumer type equipment but consumers expect it to work out of the box.
In order to achieve both full internet speed and fully capable speeds to devices, two things must be done. The first is hardware offloading and the second is disabling smart queue for traffic-policy . For the Edgerouter series, both must be done by CLI which is extremely simple. Googling each will give you clear instructions for the router you have.
More often than not, it is not the iPhone but something simple like this in the home network that consumers would never suspect nor ever know how to fix. If not on a home network then one must accept the Wi-Fi speeds provided and recognize it isn’t typically the iPhone.
Best wishes!