Geoff Ice :
Well, since you CAN get wifi, just not a good signal, I would suspect the antenna either has a bad/dirty connection, or it has failed and needs replacing. The guide below shows the general disassembly process for the IPhone 6. The antenna in question is mentioned at step 14. You could try disassembling your phone, cleaning the antenna connection points with some rubbing alcohol, and putting it back together. Just don't touch any surface you clean, as oils from your fingers can cause a bad connection. You could also opt to replace the antenna up front and see if that fixes the problem. This is all assuming that you think you can do it safely and without breaking your phone. Every repair has its risks of breaking another part, but it feels great when it goes together perfectly. You could also wait and see if someone else has a better opinion, as I am fairly new to the game.