Hey there Frenchy3745,
We understand that Wi-Fi on your iPhone is not connecting even though other devices will connect to the same network. It briefly shows the Wi-Fi symbol in the status bar, then disappears. We know Wi-Fi is critical. Let's check this out together.
To begin, it sounds like you went through the steps here already: If your iPhone, iPad, or iPod touch won’t connect to a Wi-Fi network
However, we'd like provide that just to make sure nothing is missed.
Also, we know you mentioned other devices are connecting OK, but we'd like to have you test with a different Wi-Fi network just to isolate further. If you can connect to another network, make sure to restart your wireless router and modem as mentioned in step 5 of the article above. This may help refresh the connection with your device specifically.
If it's still not working, let us know what you see when you go to: Settings > Wi-Fi
For example, is there a spinning gear, are there no networks at all, or something else?
Cheers!