iPhone 6 only detecting some WiFi networks

I have two iPhone 6 phones.

In my home I can see around 15 WiFi networks when I go to connect on one, but on the other phone I only see around 3. Both phones are in the same location, same network.

I've tried restoring / updating the iPhone and resetting network settings but nothing helps.

Anyone come accross an issue like this before? Could it be a damaged antenna?

Cellular connection and Bluetooth works perfectly, the wifi connection just seems to have a very short detection range. But when connected to my home WiFi, speed tests are the same as the phone with no issues.

Also, it's not in warrenty and I'm compitent enough to do basic/mid skill level repairs if I know what the problem is...