I have to be right next to my router for my iPhone 6 to work

So, I got a new iPhone 6 for Christmas but the Wi-Fi doesn't work unless I'm right beside the router. I've tried it in shops/mates houses and it's the luck of the draw I guess, sometimes it works, others it doesn't (as in, in some places) I've reset factory/network settings and Munich router TOO many times!
Can anyone help before I send the phone back to Apple?

This sounds like a typical case of incompatibility between your iPhone and your router's Wi-Fi. Symptoms vary between not even detecting the network right through to slow, or erratic connections.

It sounds as though your phone has problems with some but not all other Wi-Fi networks. Your best solution is to install a Wireless Access Point connected to your router. Set the WAP to use the same Wi-Fi settings as the router, then turn off the router's own Wi-Fi.

Check out different WAPs to find one that works properly with your phone.

There's an alternative, set the WAP with a different network name (SSID) and use that just for your phone keeping the existing network for other devices. Make sure the WAP and router are operating a minimum of 4 channels apart.

There are a couple of tweaks that you can do that might help this known problem;
https://www.igeeksblog.com/ios-6-wifi-problems/
Somewhere to start I suppose, regards, Bob UK.

Snapped antenna, do the sending back As soon as possible.