Mobile Phone USB Tether for Router WAN Connection

My ADSL speed is lousy, so when I need more bandwidth I tether a mobile phone to the router's Ethernet WAN port to provide faster access via 4G.<br/>
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I'd been using an Android phone connected to a Raspberry PI USB port with the Ethernet port on the PI then connected to the Ethernet WAN port on the router. Set up bridge-utils on the PI and it works perfectly.<br/>
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I swapped to an iPhone, and this didn't work, because the Android phone appeared on the PI as a USB device and the iPhone appears as an Ethernet device. Added the iPhone Ethernet device to the bridge-utils configuration and that works.<br/>
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But it would be great if it was possible just to connect a phone's USB port to the router's USB port and have the phone appear as a device. <br/>
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I came across this <URL url="https://www.visus.pt/mirrors/draytek/tools/iPhone%20Utility/Internet%20backupsharing%20by%20iPhone%203G3Gs.pdf"> <LINK_TEXT text="https://www.visus.pt/mirrors/draytek/to ... 03G3Gs.pdf">https://www.visus.pt/mirrors/draytek/tools/iPhone%20Utility/Internet%20backupsharing%20by%20iPhone%203G3Gs.pdf</LINK_TEXT> </URL> which suggests that once upon a time, it was possible, but on testing I couldn't get this to work.<br/>
It would be great if there is an up-to-date version of this; am I correct in understanding that there's not?